Wireless energy transfer for implantable devices

ABSTRACT

Wireless energy transfer apparatus include, in at least one aspect, a device resonator configured to supply power for a load by receiving wirelessly transferred power from a source resonator; a temperature sensor positioned to measure a temperature of a component of the apparatus; a tunable component coupled to the device resonator to adjust a resonant frequency of the device resonator, an effective impedance the device resonator, or both; and control circuitry configured to, in response to detecting a temperature condition using the temperature sensor, (i) tune the tunable component to adjust the resonant frequency of the device resonator, the effective impedance of the device resonator, or both, and (ii) signal the source resonator regarding the temperature condition to cause an adjustment of a resonant frequency of the source resonator, a power output of the source resonator, or both.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of (and claims thebenefit of priority to) U.S. application Ser. No. 14/496,433 filed Sep.25, 2014, which is a continuation application of (and claims the benefitof priority to) U.S. application Ser. No. 13/961,249 filed Aug. 7, 2013,now U.S. Pat. No. 8,847,548, which is a divisional application of (andclaims the benefit of priority to) U.S. application Ser. No. 13/154,131filed Jun. 6, 2011, which claims the benefit of U.S. Provisional Appl.No. 61/351,492 filed Jun. 4, 2010.

U.S. application Ser. No. 13/154,131 filed Jun. 6, 2011 is acontinuation-in-part of U.S. Ser. No. 13/090,369 filed Apr. 20, 2011which claims the benefit of U.S. Provisional Appl. No. 61/326,051 filedApr. 20, 2010.

The Ser. No. 13/090,369 application is a continuation-in-part of U.S.patent application Ser. No. 13/021,965 filed Feb. 7, 2011 which is acontinuation-in-part of U.S. patent application Ser. No. 12/986,018filed Jan. 6, 2011, which claims the benefit of U.S. Provisional Appl.No. 61/292,768 filed Jan. 6, 2010.

U.S. application Ser. No. 13/154,131 filed Jun. 6, 2011 is acontinuation-in-part of U.S. patent application Ser. No. 12/986,018filed Jan. 6, 2011 which claims the benefit of U.S. Provisional Appl.No. U.S. 61/292,768 filed Jan. 6, 2010.

The Ser. No. 12/986,018 application is a continuation-in-part of U.S.patent application Ser. No. 12/789,611 filed May 28, 2010.

The Ser. No. 12/789,611 application is a continuation-in-part of U.S.patent application Ser. No. 12/770,137 filed Apr. 29, 2010 which claimsthe benefit of U.S. Provisional Application No. 61/173,747 filed Apr.29, 2009.

The Ser. No. 12/770,137 application is a continuation-in-part of U.S.application Ser. No. 12/767,633 filed Apr. 26, 2010, which claims thebenefit of U.S. Provisional Application No. 61/172,633 filed Apr. 24,2009.

Application Ser. No. 12/767,633 is a continuation-in-part of U.S.application Ser. No. 12/759,047 filed Apr. 13, 2010 which is acontinuation-in-part of U.S. application Ser. No. 12/757,716 filed Apr.9, 2010, which is a continuation-in-part of U.S. application Ser. No.12/749,571 filed Mar. 30, 2010.

The Ser. No. 12/749,571 application is a continuation-in-part of thefollowing U.S. Applications: U.S. application Ser. No. 12/639,489 filedDec. 16, 2009; and U.S. application Ser. No. 12/647,705 filed Dec. 28,2009.

The Ser. No. 12/749,571 application a continuation-in-part of U.S.application Ser. No. 12/567,716 filed Sep. 25, 2009, which claims thebenefit of the following U.S. patent applications: U.S. App. No.61/100,721 filed Sep. 27, 2008; U.S. App. No. 61/108,743 filed Oct. 27,2008; U.S. App. No. 61/147,386 filed Jan. 26, 2009; U.S. App. No.61/152,086 filed Feb. 12, 2009; U.S. App. No. 61/178,508 filed May 15,2009; U.S. App. No. 61/182,768 filed Jun. 1, 2009; U.S. App. No.61/121,159 filed Dec. 9, 2008; U.S. App. No. 61/142,977 filed Jan. 7,2009; U.S. App. No. 61/142,885 filed Jan. 6, 2009; U.S. App. No.61/142,796 filed Jan. 6, 2009; U.S. App. No. 61/142,889 filed Jan. 6,2009; U.S. App. No. 61/142,880 filed Jan. 6, 2009; U.S. App. No.61/142,818 filed Jan. 6, 2009; U.S. App. No. 61/142,887 filed Jan. 6,2009; U.S. App. No. 61/156,764 filed Mar. 2, 2009; U.S. App. No.61/143,058 filed Jan. 7, 2009; U.S. App. No. 61/163,695 filed Mar. 26,2009; U.S. App. No. 61/172,633 filed Apr. 24, 2009; U.S. App. No.61/169,240 filed Apr. 14, 2009, U.S. App. No. 61/173,747 filed Apr. 29,2009.

The Ser. No. 12/757,716 application is a continuation-in-part of U.S.application Ser. No. 12/721,118 filed Mar. 10, 2010, which is acontinuation-in-part of U.S. application Ser. No. 12/705,582 filed Feb.13, 2010 which claims the benefit of U.S. Provisional Application No.61/152,390 filed Feb. 13, 2009.

Each of the foregoing applications is incorporated herein by referencein its entirety.

BACKGROUND

Field

This disclosure relates to wireless energy transfer, methods, systemsand apparati to accomplish such transfer, and applications.

Description of the Related Art

Energy or power may be transferred wirelessly using a variety oftechniques as detailed, for example, in commonly owned U.S. patentapplication Ser. No. 12/789,611 published on Sep. 23, 2010 as U.S. Pat.Pub. No. 2010/0237709 and entitled “RESONATOR ARRAYS FOR WIRELESS ENERGYTRANSFER,” and U.S. patent application Ser. No. 12/722,050 published onJul. 22, 2010 as U.S. Pat. Pub. No. 2010/0181843 and entitled “WIRELESSENERGY TRANSFER FOR REFRIGERATOR APPLICATION” the contents of which areincorporated in their entirety as if fully set forth herein. Prior artwireless energy transfer systems have been limited by a variety offactors including concerns over user safety, low energy transferefficiencies and restrictive physical proximity/alignment tolerances forthe energy supply and sink components.

Implantable devices such as mechanical circulatory support (MCS)devices, ventricular assist device (VAD), implantable cardioverterdefibrillators (ICD), and the like may require an external energy sourcefor operation for extended period of time. In some patients andsituations the implanted device requires constant or near constantoperation and has considerable power demands that require connection toan external power source requiring percutaneous cables or cables that gothrough the skin of the patient to an external power source increasingthe possibility of infection and decreasing patient comfort.

Therefore a need exists for methods and designs for energy delivery toimplanted devices without requiring direct wire connections.

SUMMARY

Various systems and processes, in various embodiments, provide wirelessenergy transfer using coupled resonators. In some embodiments, theresonator structures may require or benefit from thermal management ofthe components of the resonators. Resonator components may requirecooling to prevent their temperatures from exceeding a criticaltemperature. The features of such embodiments are general and may beapplied to a wide range of resonators, regardless of the specificexamples discussed herein.

In embodiments, a magnetic resonator may comprise some combination ofinductors and capacitors. Additional circuit elements such ascapacitors, inductors, resistors, switches, and the like, may beinserted between a magnetic resonator and a power source, and/or betweena magnetic resonator and a power load. In this disclosure, theconducting coil that comprises the high-Q inductive loop of theresonator may be referred to as the inductor and/or the inductive load.The inductive load may also refer to the inductor when it is wirelesslycoupled (through a mutual inductance) to other system or extraneousobjects. In this disclosure, circuit elements other than the inductiveload may be referred to as being part of an impedance matching networkor IMN. It is to be understood that all, some, or none of the elementsthat are referred to as being part of an impedance matching network maybe part of the magnetic resonator. Which elements are part of theresonator and which are separate from the resonator will depend on thespecific magnetic resonator and wireless energy transfer system design.

In embodiments, wireless energy transfer described herein may be used todeliver power to the implanted device without requiring through the skinwiring. In embodiments wireless power transfer may be used toperiodically or continuously power or recharge an implanted rechargeablebattery, super capacitor, or other energy storage component.

In embodiments the wireless energy transfer described herein improvesthe range and tolerable offset of source and device resonators with theuse of repeater resonators that may be internal or external to apatient.

In embodiments, the source and device resonators may control thedistribution of heat and energy dissipation by tuning elements of thesource and the device.

Unless otherwise indicated, this disclosure uses the terms wirelessenergy transfer, wireless power transfer, wireless power transmission,and the like, interchangeably. Those skilled in the art will understandthat a variety of system architectures may be supported by the widerange of wireless system designs and functionalities described in thisapplication.

In the wireless energy transfer systems described herein, power may beexchanged wirelessly between at least two resonators. Resonators maysupply, receive, hold, transfer, and distribute energy. Sources ofwireless power may be referred to as sources or supplies and receiversof wireless power may be referred to as devices, receivers and powerloads. A resonator may be a source, a device, or both, simultaneously ormay vary from one function to another in a controlled manner. Resonatorsconfigured to hold or distribute energy that do not have wiredconnections to a power supply or power drain may be called repeaters.

The resonators of the wireless energy transfer systems of this inventionare able to transfer power over distances that are large compared to thesize of the resonators themselves. That is, if the resonator size ischaracterized by the radius of the smallest sphere that could enclosethe resonator structure, the wireless energy transfer system of thisinvention can transfer power over distances greater than thecharacteristic size of a resonator. The system is able to exchangeenergy between resonators where the resonators have differentcharacteristic sizes and where the inductive elements of the resonatorshave different sizes, different shapes, are comprised of differentmaterials, and the like.

The wireless energy transfer systems of this invention may be describedas having a coupling region, an energized area or volume, all by way ofdescribing that energy may be transferred between resonant objects thatare separated from each other, they may have variable distance from eachother, and that may be moving relative to each other. In someembodiments, the area or volume over which energy can be transferred isreferred to as the active field area or volume. In addition, thewireless energy transfer system may comprise more than two resonatorsthat may each be coupled to a power source, a power load, both, orneither.

Wirelessly supplied energy may be used to power electric or electronicequipment, recharge batteries or charge energy storage units. Multipledevices may be charged or powered simultaneously or power delivery tomultiple devices may be serialized such that one or more devices receivepower for a period of time after which power delivery may be switched toother devices. In various embodiments, multiple devices may share powerfrom one or more sources with one or more other devices eithersimultaneously, or in a time multiplexed manner, or in a frequencymultiplexed manner, or in a spatially multiplexed manner, or in anorientation multiplexed manner, or in any combination of time andfrequency and spatial and orientation multiplexing. Multiple devices mayshare power with each other, with at least one device being reconfiguredcontinuously, intermittently, periodically, occasionally, ortemporarily, to operate as a wireless power source. Those of ordinaryskill in the art will understand that there are a variety of ways topower and/or charge devices applicable to the technologies andapplications described herein.

This disclosure references certain individual circuit components andelements such as capacitors, inductors, resistors, diodes, transformers,switches and the like; combinations of these elements as networks,topologies, circuits, and the like; and objects that have inherentcharacteristics such as “self-resonant” objects with capacitance orinductance distributed (or partially distributed, as opposed to solelylumped) throughout the entire object. It would be understood by one ofordinary skill in the art that adjusting and controlling variablecomponents within a circuit or network may adjust the performance ofthat circuit or network and that those adjustments may be describedgenerally as tuning, adjusting, matching, correcting, and the like.Other methods to tune or adjust the operating point of the wirelesspower transfer system may be used alone, or in addition to adjustingtunable components such as inductors and capacitors, or banks ofinductors and capacitors. Those skilled in the art will recognize that aparticular topology discussed in this disclosure can be implemented in avariety of other ways.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. In case of conflict withpublications, patent applications, patents, and other referencesmentioned or incorporated herein by reference, the presentspecification, including definitions, will control.

Any of the features described above may be used, alone or incombination, without departing from the scope of this disclosure. Otherfeatures, objects, and advantages of the systems and methods disclosedherein will be apparent from the following detailed description andfigures.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a system block diagram of wireless energy transferconfigurations.

FIGS. 2A-2F are exemplary structures and schematics of simple resonatorstructures.

FIG. 3 is a block diagram of a wireless source with a single-endedamplifier.

FIG. 4 is a block diagram of a wireless source with a differentialamplifier.

FIGS. 5A and 5B are block diagrams of sensing circuits.

FIGS. 6A, 6B, and 6C are block diagrams of a wireless source.

FIG. 7 is a plot showing the effects of a duty cycle on the parametersof an amplifier.

FIG. 8 is a simplified circuit diagram of a wireless power source with aswitching amplifier.

FIG. 9 shows plots of the effects of changes of parameters of a wirelesspower source.

FIG. 10 shows plots of the effects of changes of parameters of awireless power source.

FIGS. 11A, 11B, and 11C are plots showing the effects of changes ofparameters of a wireless power source.

FIG. 12 shows plots of the effects of changes of parameters of awireless power source.

FIG. 13 is a simplified circuit diagram of a wireless energy transfersystem comprising a wireless power source with a switching amplifier anda wireless power device.

FIG. 14 shows plots of the effects of changes of parameters of awireless power source.

FIG. 15 is a diagram of a resonator showing possible nonuniform magneticfield distributions due to irregular spacing between tiles of magneticmaterial.

FIG. 16 is a resonator with an arrangement of tiles in a block ofmagnetic material that may reduce hotspots in the magnetic materialblock.

FIG. 17A is a resonator with a block of magnetic material comprisingsmaller individual tiles and 17B and 17C is the resonator withadditional strips of thermally conductive material used for thermalmanagement.

FIG. 18 is an embodiment of a surgical robot and a hospital bed withwireless energy sources and devices.

FIG. 19 is an embodiment of a surgical robot and a hospital bed withwireless energy sources and devices.

FIG. 20A is a medical cart with a wireless energy transfer resonator.FIG. 20B is a computer cart with a wireless energy transfer resonator.

FIG. 21 is a diagram of a wirelessly powered cauterizing tool.

FIGS. 22A and 22B are block diagrams of a wireless power transfer systemfor implantable devices.

FIGS. 23A, 23B, 23C, and 23D are diagrams depicting source and deviceconfigurations of wireless energy transfer for implantable devices.

DETAILED DESCRIPTION

As described above, this disclosure relates to wireless energy transferusing coupled electromagnetic resonators. However, such energy transferis not restricted to electromagnetic resonators, and the wireless energytransfer systems described herein are more general and may beimplemented using a wide variety of resonators and resonant objects.

As those skilled in the art will recognize, important considerations forresonator-based power transfer include resonator efficiency andresonator coupling. Extensive discussion of such issues, e.g., coupledmode theory (CMT), coupling coefficients and factors, quality factors(also referred to as Q-factors), and impedance matching is provided, forexample, in U.S. patent application Ser. No. 12/789,611 published onSep. 23, 2010 as US 20100237709 and entitled “RESONATOR ARRAYS FORWIRELESS ENERGY TRANSFER,” and U.S. patent application Ser. No.12/722,050 published on Jul. 22, 2010 as US 20100181843 and entitled“WIRELESS ENERGY TRANSFER FOR REFRIGERATOR APPLICATION” and incorporatedherein by reference in its entirety as if fully set forth herein.

A resonator may be defined as a resonant structure that can store energyin at least two different forms, and where the stored energy oscillatesbetween the two forms. The resonant structure will have a specificoscillation mode with a resonant (modal) frequency, f, and a resonant(modal) field. The angular resonant frequency, ω, may be defined asω=2πf the resonant period, T, may be defined as T=1/f=2π/ω, and theresonant wavelength, λ, may be defined as λ=c/f, where c is the speed ofthe associated field waves (light, for electromagnetic resonators). Inthe absence of loss mechanisms, coupling mechanisms or external energysupplying or draining mechanisms, the total amount of energy stored bythe resonator, W, would stay fixed, but the form of the energy wouldoscillate between the two forms supported by the resonator, wherein oneform would be maximum when the other is minimum and vice versa.

For example, a resonator may be constructed such that the two forms ofstored energy are magnetic energy and electric energy. Further, theresonator may be constructed such that the electric energy stored by theelectric field is primarily confined within the structure while themagnetic energy stored by the magnetic field is primarily in the regionsurrounding the resonator. In other words, the total electric andmagnetic energies would be equal, but their localization would bedifferent. Using such structures, energy exchange between at least twostructures may be mediated by the resonant magnetic near-field of the atleast two resonators. These types of resonators may be referred to asmagnetic resonators.

An important parameter of resonators used in wireless power transmissionsystems is the Quality Factor, or Q-factor, or Q, of the resonator,which characterizes the energy decay and is inversely proportional toenergy losses of the resonator. It may be defined as Q=ω*W/P, where P isthe time-averaged power lost at steady state. That is, a resonator witha high-Q has relatively low intrinsic losses and can store energy for arelatively long time. Since the resonator loses energy at its intrinsicdecay rate, 2Γ, its Q, also referred to as its intrinsic Q, is given byQ=ω/2Γ. The quality factor also represents the number of oscillationperiods, T, it takes for the energy in the resonator to decay by afactor of e^(−2π). Note that the quality factor or intrinsic qualityfactor or Q of the resonator is that due only to intrinsic lossmechanisms. The Q of a resonator connected to, or coupled to a powergenerator, g, or load, l, may be called the “loaded quality factor” orthe “loaded Q”. The Q of a resonator in the presence of an extraneousobject that is not intended to be part of the energy transfer system maybe called the “perturbed quality factor” or the “perturbed Q”.

Resonators, coupled through any portion of their near-fields mayinteract and exchange energy. The efficiency of this energy transfer canbe significantly enhanced if the resonators operate at substantially thesame resonant frequency. By way of example, but not limitation, imaginea source resonator with Q_(s) and a device resonator with Q_(d). High-Qwireless energy transfer systems may utilize resonators that are high-Q.The Q of each resonator may be high. The geometric mean of the resonatorQ's, √{square root over (Q_(s)Q_(d))} may also or instead be high.

The coupling factor, k, is a number between 0≤|k|≤1, and it may beindependent (or nearly independent) of the resonant frequencies of thesource and device resonators, when those are placed at sub-wavelengthdistances. Rather the coupling factor k may be determined mostly by therelative geometry and the distance between the source and deviceresonators where the physical decay-law of the field mediating theircoupling is taken into account. The coupling coefficient used in CMT,κ=√{square root over (ω_(s)ω_(d))}/2, may be a strong function of theresonant frequencies, as well as other properties of the resonatorstructures. In applications for wireless energy transfer utilizing thenear-fields of the resonators, it is desirable to have the size of theresonator be much smaller than the resonant wavelength, so that powerlost by radiation is reduced. In some embodiments, high-Q resonators aresub-wavelength structures. In some electromagnetic embodiments, high-Qresonator structures are designed to have resonant frequencies higherthan 100 kHz. In other embodiments, the resonant frequencies may be lessthan 1 GHz.

In exemplary embodiments, the power radiated into the far-field by thesesub wavelength resonators may be further reduced by lowering theresonant frequency of the resonators and the operating frequency of thesystem. In other embodiments, the far field radiation may be reduced byarranging for the far fields of two or more resonators to interferedestructively in the far field.

In a wireless energy transfer system a resonator may be used as awireless energy source, a wireless energy capture device, a repeater ora combination thereof. In embodiments a resonator may alternate betweentransferring energy, receiving energy or relaying energy. In a wirelessenergy transfer system one or more magnetic resonators may be coupled toan energy source and be energized to produce an oscillating magneticnear-field. Other resonators that are within the oscillating magneticnear-fields may capture these fields and convert the energy intoelectrical energy that may be used to power or charge a load therebyenabling wireless transfer of useful energy.

The so-called “useful” energy in a useful energy exchange is the energyor power that must be delivered to a device in order to power or chargeit at an acceptable rate. The transfer efficiency that corresponds to auseful energy exchange may be system or application-dependent. Forexample, high power vehicle charging applications that transferkilowatts of power may need to be at least 80% efficient in order tosupply useful amounts of power resulting in a useful energy exchangesufficient to recharge a vehicle battery without significantly heatingup various components of the transfer system. In some consumerelectronics applications, a useful energy exchange may include anyenergy transfer efficiencies greater than 10%, or any other amountacceptable to keep rechargeable batteries “topped off” and running forlong periods of time. In implanted medical device applications, a usefulenergy exchange may be any exchange that does not harm the patient butthat extends the life of a battery or wakes up a sensor or monitor orstimulator. In such applications, 100 mW of power or less may be useful.In distributed sensing applications, power transfer of microwatts may beuseful, and transfer efficiencies may be well below 1%.

A useful energy exchange for wireless energy transfer in a powering orrecharging application may be efficient, highly efficient, or efficientenough, as long as the wasted energy levels, heat dissipation, andassociated field strengths are within tolerable limits and are balancedappropriately with related factors such as cost, weight, size, and thelike.

The resonators may be referred to as source resonators, deviceresonators, first resonators, second resonators, repeater resonators,and the like. Implementations may include three (3) or more resonators.For example, a single source resonator may transfer energy to multipledevice resonators or multiple devices. Energy may be transferred from afirst device to a second, and then from the second device to the third,and so forth. Multiple sources may transfer energy to a single device orto multiple devices connected to a single device resonator or tomultiple devices connected to multiple device resonators. Resonators mayserve alternately or simultaneously as sources, devices, and/or they maybe used to relay power from a source in one location to a device inanother location. Intermediate electromagnetic resonators may be used toextend the distance range of wireless energy transfer systems and/or togenerate areas of concentrated magnetic near-fields. Multiple resonatorsmay be daisy-chained together, exchanging energy over extended distancesand with a wide range of sources and devices. For example, a sourceresonator may transfer power to a device resonator via several repeaterresonators. Energy from a source may be transferred to a first repeaterresonator, the first repeater resonator may transfer the power to asecond repeater resonator and the second to a third and so on until thefinal repeater resonator transfers its energy to a device resonator. Inthis respect the range or distance of wireless energy transfer may beextended and/or tailored by adding repeater resonators. High powerlevels may be split between multiple sources, transferred to multipledevices and recombined at a distant location.

The resonators may be designed using coupled mode theory models, circuitmodels, electromagnetic field models, and the like. The resonators maybe designed to have tunable characteristic sizes. The resonators may bedesigned to handle different power levels. In exemplary embodiments,high power resonators may require larger conductors and higher currentor voltage rated components than lower power resonators.

FIG. 1 shows a diagram of exemplary configurations and arrangements of awireless energy transfer system. A wireless energy transfer system mayinclude at least one source resonator (R1) 104 (optionally R6, 112)coupled to an energy source 102 and optionally a sensor and control unit108. The energy source may be a source of any type of energy capable ofbeing converted into electrical energy that may be used to drive thesource resonator 104. The energy source may be a battery, a solar panel,the electrical mains, a wind or water turbine, an electromagneticresonator, a generator, and the like. The electrical energy used todrive the magnetic resonator is converted into oscillating magneticfields by the resonator. The oscillating magnetic fields may be capturedby other resonators which may be device resonators (R2) 106, (R3) 116that are optionally coupled to an energy drain 110. The oscillatingfields may be optionally coupled to repeater resonators (R4, R5) thatare configured to extend or tailor the wireless energy transfer region.Device resonators may capture the magnetic fields in the vicinity ofsource resonator(s), repeater resonators and other device resonators andconvert them into electrical energy that may be used by an energy drain.The energy drain 110 may be an electrical, electronic, mechanical orchemical device and the like configured to receive electrical energy.Repeater resonators may capture magnetic fields in the vicinity ofsource, device and repeater resonator(s) and may pass the energy on toother resonators.

A wireless energy transfer system may comprise a single source resonator104 coupled to an energy source 102 and a single device resonator 106coupled to an energy drain 110. In embodiments a wireless energytransfer system may comprise multiple source resonators coupled to oneor more energy sources and may comprise multiple device resonatorscoupled to one or more energy drains.

In embodiments the energy may be transferred directly between a sourceresonator 104 and a device resonator 106. In other embodiments theenergy may be transferred from one or more source resonators 104, 112 toone or more device resonators 106, 116 via any number of intermediateresonators which may be device resonators, source resonators, repeaterresonators, and the like. Energy may be transferred via a network orarrangement of resonators 114 that may include subnetworks 118, 120arranged in any combination of topologies such as token ring, mesh, adhoc, and the like.

In embodiments the wireless energy transfer system may comprise acentralized sensing and control system 108. In embodiments parameters ofthe resonators, energy sources, energy drains, network topologies,operating parameters, etc. may be monitored and adjusted from a controlprocessor to meet specific operating parameters of the system. A centralcontrol processor may adjust parameters of individual components of thesystem to optimize global energy transfer efficiency, to optimize theamount of power transferred, and the like. Other embodiments may bedesigned to have a substantially distributed sensing and control system.Sensing and control may be incorporated into each resonator or group ofresonators, energy sources, energy drains, and the like and may beconfigured to adjust the parameters of the individual components in thegroup to maximize the power delivered, to maximize energy transferefficiency in that group and the like.

In embodiments, components of the wireless energy transfer system mayhave wireless or wired data communication links to other components suchas devices, sources, repeaters, power sources, resonators, and the likeand may transmit or receive data that can be used to enable thedistributed or centralized sensing and control. A wireless communicationchannel may be separate from the wireless energy transfer channel, or itmay be the same. In one embodiment the resonators used for powerexchange may also be used to exchange information. In some cases,information may be exchanged by modulating a component in a source ordevice circuit and sensing that change with port parameter or othermonitoring equipment. Resonators may signal each other by tuning,changing, varying, dithering, and the like, the resonator parameterssuch as the impedance of the resonators which may affect the reflectedimpedance of other resonators in the system. The systems and methodsdescribed herein may enable the simultaneous transmission of power andcommunication signals between resonators in wireless power transmissionsystems, or it may enable the transmission of power and communicationsignals during different time periods or at different frequencies usingthe same magnetic fields that are used during the wireless energytransfer. In other embodiments wireless communication may be enabledwith a separate wireless communication channel such as WiFi, Bluetooth,Infrared, and the like.

In embodiments, a wireless energy transfer system may include multipleresonators and overall system performance may be improved by control ofvarious elements in the system. For example, devices with lower powerrequirements may tune their resonant frequency away from the resonantfrequency of a high-power source that supplies power to devices withhigher power requirements. In this way, low and high power devices maysafely operate or charge from a single high power source. In addition,multiple devices in a charging zone may find the power available to themregulated according to any of a variety of consumption controlalgorithms such as First-Come-First-Serve, Best Effort, GuaranteedPower, etc. The power consumption algorithms may be hierarchical innature, giving priority to certain users or types of devices, or it maysupport any number of users by equally sharing the power that isavailable in the source. Power may be shared by any of the multiplexingtechniques described in this disclosure.

In embodiments electromagnetic resonators may be realized or implementedusing a combination of shapes, structures, and configurations.Electromagnetic resonators may include an inductive element, adistributed inductance, or a combination of inductances with a totalinductance, L, and a capacitive element, a distributed capacitance, or acombination of capacitances, with a total capacitance, C. A minimalcircuit model of an electromagnetic resonator comprising capacitance,inductance and resistance, is shown in FIG. 2F. The resonator mayinclude an inductive element 238 and a capacitive element 240. Providedwith initial energy, such as electric field energy stored in thecapacitor 240, the system will oscillate as the capacitor dischargestransferring energy into magnetic field energy stored in the inductor238 which in turn transfers energy back into electric field energystored in the capacitor 240. Intrinsic losses in these electromagneticresonators include losses due to resistance in the inductive andcapacitive elements and to radiation losses, and are represented by theresistor, R, 242 in FIG. 2F.

FIG. 2A shows a simplified drawing of an exemplary magnetic resonatorstructure. The magnetic resonator may include a loop of conductor actingas an inductive element 202 and a capacitive element 204 at the ends ofthe conductor loop. The inductor 202 and capacitor 204 of anelectromagnetic resonator may be bulk circuit elements, or theinductance and capacitance may be distributed and may result from theway the conductors are formed, shaped, or positioned, in the structure.

For example, the inductor 202 may be realized by shaping a conductor toenclose a surface area, as shown in FIG. 2A. This type of resonator maybe referred to as a capacitively-loaded loop inductor. Note that we mayuse the terms “loop” or “coil” to indicate generally a conductingstructure (wire, tube, strip, etc.), enclosing a surface of any shapeand dimension, with any number of turns. In FIG. 2A, the enclosedsurface area is circular, but the surface may be any of a wide varietyof other shapes and sizes and may be designed to achieve certain systemperformance specifications. In embodiments the inductance may berealized using inductor elements, distributed inductance, networks,arrays, series and parallel combinations of inductors and inductances,and the like. The inductance may be fixed or variable and may be used tovary impedance matching as well as resonant frequency operatingconditions.

There are a variety of ways to realize the capacitance required toachieve the desired resonant frequency for a resonator structure.Capacitor plates 204 may be formed and utilized as shown in FIG. 2A, orthe capacitance may be distributed and be realized between adjacentwindings of a multi-loop conductor. The capacitance may be realizedusing capacitor elements, distributed capacitance, networks, arrays,series and parallel combinations of capacitances, and the like. Thecapacitance may be fixed or variable and may be used to vary impedancematching as well as resonant frequency operating conditions.

The inductive elements used in magnetic resonators may contain more thanone loop and may spiral inward or outward or up or down or in somecombination of directions. In general, the magnetic resonators may havea variety of shapes, sizes and number of turns and they may be composedof a variety of conducing materials. The conductor 210, for example, maybe a wire, a Litz wire, a ribbon, a pipe, a trace formed from conductingink, paint, gels, and the like or from single or multiple traces printedon a circuit board. An exemplary embodiment of a trace pattern on asubstrate 208 forming inductive loops is depicted in FIG. 2B.

In embodiments the inductive elements may be formed using magneticmaterials of any size, shape thickness, and the like, and of materialswith a wide range of permeability and loss values. These magneticmaterials may be solid blocks, they may enclose hollow volumes, they maybe formed from many smaller pieces of magnetic material tiled and orstacked together, and they may be integrated with conducting sheets orenclosures made from highly conducting materials. Conductors may bewrapped around the magnetic materials to generate the magnetic field.These conductors may be wrapped around one or more than one axis of thestructure. Multiple conductors may be wrapped around the magneticmaterials and combined in parallel, or in series, or via a switch toform customized near-field patterns and/or to orient the dipole momentof the structure. Examples of resonators comprising magnetic materialare depicted in FIGS. 2C, 2D, 2E. In FIG. 2D the resonator comprisesloops of conductor 224 wrapped around a core of magnetic material 222creating a structure that has a magnetic dipole moment 228 that isparallel to the axis of the loops of the conductor 224. The resonatormay comprise multiple loops of conductor 216, 212 wrapped in orthogonaldirections around the magnetic material 214 forming a resonator with amagnetic dipole moment 218, 220 that may be oriented in more than onedirection as depicted in FIG. 2C, depending on how the conductors aredriven.

An electromagnetic resonator may have a characteristic, natural, orresonant frequency determined by its physical properties. This resonantfrequency is the frequency at which the energy stored by the resonatoroscillates between that stored by the electric field, W_(E),(W_(E)=q²/2C, where q is the charge on the capacitor, C) and that storedby the magnetic field, W_(B), (W_(B)=Li²/2, where i is the currentthrough the inductor, L) of the resonator. The frequency at which thisenergy is exchanged may be called the characteristic frequency, thenatural frequency, or the resonant frequency of the resonator, and isgiven by ω,

$\omega = {{2\pi\; f} = {\sqrt{\frac{1}{LC}}.}}$The resonant frequency of the resonator may be changed by tuning theinductance, L, and/or the capacitance, C, of the resonator. In oneembodiment system parameters are dynamically adjustable or tunable toachieve as close as possible to optimal operating conditions. However,based on the discussion above, efficient enough energy exchange may berealized even if some system parameters are not variable or componentsare not capable of dynamic adjustment.

In embodiments a resonator may comprise an inductive element coupled tomore than one capacitor arranged in a network of capacitors and circuitelements. In embodiments the coupled network of capacitors and circuitelements may be used to define more than one resonant frequency of theresonator. In embodiments a resonator may be resonant, or partiallyresonant, at more than one frequency.

In embodiments, a wireless power source may comprise of at least oneresonator coil coupled to a power supply, which may be a switchingamplifier, such as a class-D amplifier or a class-E amplifier or acombination thereof. In this case, the resonator coil is effectively apower load to the power supply. In embodiments, a wireless power devicemay comprise of at least one resonator coil coupled to a power load,which may be a switching rectifier, such as a class-D rectifier or aclass-E rectifier or a combination thereof. In this case, the resonatorcoil is effectively a power supply for the power load, and the impedanceof the load directly relates also to the work-drainage rate of the loadfrom the resonator coil. The efficiency of power transmission between apower supply and a power load may be impacted by how closely matched theoutput impedance of the power source is to the input impedance of theload. Power may be delivered to the load at a maximum possibleefficiency, when the input impedance of the load is equal to the complexconjugate of the internal impedance of the power supply. Designing thepower supply or power load impedance to obtain a maximum powertransmission efficiency is often called “impedance matching”, and mayalso referred to as optimizing the ratio of useful-to-lost powers in thesystem. Impedance matching may be performed by adding networks or setsof elements such as capacitors, inductors, transformers, switches,resistors, and the like, to form impedance matching networks between apower supply and a power load. In embodiments, mechanical adjustmentsand changes in element positioning may be used to achieve impedancematching. For varying loads, the impedance matching network may includevariable components that are dynamically adjusted to ensure that theimpedance at the power supply terminals looking towards the load and thecharacteristic impedance of the power supply remain substantiallycomplex conjugates of each other, even in dynamic environments andoperating scenarios.

In embodiments, impedance matching may be accomplished by tuning theduty cycle, and/or the phase, and/or the frequency of the driving signalof the power supply or by tuning a physical component within the powersupply, such as a capacitor. Such a tuning mechanism may be advantageousbecause it may allow impedance matching between a power supply and aload without the use of a tunable impedance matching network, or with asimplified tunable impedance matching network, such as one that hasfewer tunable components for example. In embodiments, tuning the dutycycle, and/or frequency, and/or phase of the driving signal to a powersupply may yield a dynamic impedance matching system with an extendedtuning range or precision, with higher power, voltage and/or currentcapabilities, with faster electronic control, with fewer externalcomponents, and the like.

In some wireless energy transfer systems the parameters of the resonatorsuch as the inductance may be affected by environmental conditions suchas surrounding objects, temperature, orientation, number and position ofother resonators and the like. Changes in operating parameters of theresonators may change certain system parameters, such as the efficiencyof transferred power in the wireless energy transfer. For example,high-conductivity materials located near a resonator may shift theresonant frequency of a resonator and detune it from other resonantobjects. In some embodiments, a resonator feedback mechanism is employedthat corrects its frequency by changing a reactive element (e.g., aninductive element or capacitive element). In order to achieve acceptablematching conditions, at least some of the system parameters may need tobe dynamically adjustable or tunable. All the system parameters may bedynamically adjustable or tunable to achieve approximately the optimaloperating conditions. However, efficient enough energy exchange may berealized even if all or some system parameters are not variable. In someexamples, at least some of the devices may not be dynamically adjusted.In some examples, at least some of the sources may not be dynamicallyadjusted. In some examples, at least some of the intermediate resonatorsmay not be dynamically adjusted. In some examples, none of the systemparameters may be dynamically adjusted.

In some embodiments changes in parameters of components may be mitigatedby selecting components with characteristics that change in acomplimentary or opposite way or direction when subjected to differencesin operating environment or operating point. In embodiments, a systemmay be designed with components, such as capacitors, that have anopposite dependence or parameter fluctuation due to temperature, powerlevels, frequency, and the like. In some embodiments, the componentvalues as a function of temperature may be stored in a look-up table ina system microcontroller and the reading from a temperature sensor maybe used in the system control feedback loop to adjust other parametersto compensate for the temperature induced component value changes.

In some embodiments the changes in parameter values of components may becompensated with active tuning circuits comprising tunable components.Circuits that monitor the operating environment and operating point ofcomponents and system may be integrated in the design. The monitoringcircuits may provide the signals necessary to actively compensate forchanges in parameters of components. For example, a temperature readingmay be used to calculate expected changes in, or to indicate previouslymeasured values of, capacitance of the system allowing compensation byswitching in other capacitors or tuning capacitors to maintain thedesired capacitance over a range of temperatures. In embodiments, the RFamplifier switching waveforms may be adjusted to compensate forcomponent value or load changes in the system. In some embodiments thechanges in parameters of components may be compensated with activecooling, heating, active environment conditioning, and the like.

The parameter measurement circuitry may measure or monitor certainpower, voltage, and current, signals in the system, and processors orcontrol circuits may adjust certain settings or operating parametersbased on those measurements. In addition the magnitude and phase ofvoltage and current signals, and the magnitude of the power signals,throughout the system may be accessed to measure or monitor the systemperformance. The measured signals referred to throughout this disclosuremay be any combination of port parameter signals, as well as voltagesignals, current signals, power signals, temperatures signals and thelike. These parameters may be measured using analog or digitaltechniques, they may be sampled and processed, and they may be digitizedor converted using a number of known analog and digital processingtechniques. In embodiments, preset values of certain measured quantitiesare loaded in a system controller or memory location and used in variousfeedback and control loops. In embodiments, any combination of measured,monitored, and/or preset signals may be used in feedback circuits orsystems to control the operation of the resonators and/or the system.

Adjustment algorithms may be used to adjust the frequency, Q, and/orimpedance of the magnetic resonators. The algorithms may take as inputsreference signals related to the degree of deviation from a desiredoperating point for the system and may output correction or controlsignals related to that deviation that control variable or tunableelements of the system to bring the system back towards the desiredoperating point or points. The reference signals for the magneticresonators may be acquired while the resonators are exchanging power ina wireless power transmission system, or they may be switched out of thecircuit during system operation. Corrections to the system may beapplied or performed continuously, periodically, upon a thresholdcrossing, digitally, using analog methods, and the like.

In embodiments, lossy extraneous materials and objects may introducepotential reductions in efficiencies by absorbing the magnetic and/orelectric energy of the resonators of the wireless power transmissionsystem. Those impacts may be mitigated in various embodiments bypositioning resonators to minimize the effects of the lossy extraneousmaterials and objects and by placing structural field shaping elements(e.g., conductive structures, plates and sheets, magnetic materialstructures, plates and sheets, and combinations thereof) to minimizetheir effect.

One way to reduce the impact of lossy materials on a resonator is to usehigh-conductivity materials, magnetic materials, or combinations thereofto shape the resonator fields such that they avoid the lossy objects. Inan exemplary embodiment, a layered structure of high-conductivitymaterial and magnetic material may tailor, shape, direct, reorient, etc.the resonator's electromagnetic fields so that they avoid lossy objectsin their vicinity by deflecting the fields. FIG. 2D shows a top view ofa resonator with a sheet of conductor 226 below the magnetic materialthat may used to tailor the fields of the resonator so that they avoidlossy objects that may be below the sheet of conductor 226. The layer orsheet of good 226 conductor may comprise any high conductivity materialssuch as copper, silver, aluminum, as may be most appropriate for a givenapplication. In certain embodiments, the layer or sheet of goodconductor is thicker than the skin depth of the conductor at theresonator operating frequency. The conductor sheet may be preferablylarger than the size of the resonator, extending beyond the physicalextent of the resonator.

In environments and systems where the amount of power being transmittedcould present a safety hazard to a person or animal that may intrudeinto the active field volume, safety measures may be included in thesystem. In embodiments where power levels require particularized safetymeasures, the packaging, structure, materials, and the like of theresonators may be designed to provide a spacing or “keep away” zone fromthe conducting loops in the magnetic resonator. To provide furtherprotection, high-Q resonators and power and control circuitry may belocated in enclosures that confine high voltages or currents to withinthe enclosure, that protect the resonators and electrical componentsfrom weather, moisture, sand, dust, and other external elements, as wellas from impacts, vibrations, scrapes, explosions, and other types ofmechanical shock. Such enclosures call for attention to various factorssuch as thermal dissipation to maintain an acceptable operatingtemperature range for the electrical components and the resonator. Inembodiments, enclosure may be constructed of non-lossy materials such ascomposites, plastics, wood, concrete, and the like and may be used toprovide a minimum distance from lossy objects to the resonatorcomponents. A minimum separation distance from lossy objects orenvironments which may include metal objects, salt water, oil and thelike, may improve the efficiency of wireless energy transfer. Inembodiments, a “keep away” zone may be used to increase the perturbed Qof a resonator or system of resonators. In embodiments a minimumseparation distance may provide for a more reliable or more constantoperating parameters of the resonators.

In embodiments, resonators and their respective sensor and controlcircuitry may have various levels of integration with other electronicand control systems and subsystems. In some embodiments the power andcontrol circuitry and the device resonators are completely separatemodules or enclosures with minimal integration to existing systems,providing a power output and a control and diagnostics interface. Insome embodiments a device is configured to house a resonator and circuitassembly in a cavity inside the enclosure, or integrated into thehousing or enclosure of the device.

Example Resonator Circuitry

FIGS. 3 and 4 show high level block diagrams depicting power generation,monitoring, and control components for exemplary sources of a wirelessenergy transfer system. FIG. 3 is a block diagram of a source comprisinga half-bridge switching power amplifier and some of the associatedmeasurement, tuning, and control circuitry. FIG. 4 is a block diagram ofa source comprising a full-bridge switching amplifier and some of theassociated measurement, tuning, and control circuitry.

The half bridge system topology depicted in FIG. 3 may comprise aprocessing unit that executes a control algorithm 328. The processingunit executing a control algorithm 328 may be a microcontroller, anapplication specific circuit, a field programmable gate array, aprocessor, a digital signal processor, and the like. The processing unitmay be a single device or it may be a network of devices. The controlalgorithm may run on any portion of the processing unit. The algorithmmay be customized for certain applications and may comprise acombination of analog and digital circuits and signals. The masteralgorithm may measure and adjust voltage signals and levels, currentsignals and levels, signal phases, digital count settings, and the like.

The system may comprise an optional source/device and/or source/otherresonator communication controller 332 coupled to wireless communicationcircuitry 312. The optional source/device and/or source/other resonatorcommunication controller 332 may be part of the same processing unitthat executes the master control algorithm, it may a part or a circuitwithin a microcontroller 302, it may be external to the wireless powertransmission modules, it may be substantially similar to communicationcontrollers used in wire powered or battery powered applications butadapted to include some new or different functionality to enhance orsupport wireless power transmission.

The system may comprise a PWM generator 306 coupled to at least twotransistor gate drivers 334 and may be controlled by the controlalgorithm. The two transistor gate drivers 334 may be coupled directlyor via gate drive transformers to two power transistors 336 that drivethe source resonator coil 344 through impedance matching networkcomponents 342. The power transistors 336 may be coupled and poweredwith an adjustable DC supply 304 and the adjustable DC supply 304 may becontrolled by a variable bus voltage, Vbus. The Vbus controller may becontrolled by the control algorithm 328 and may be part of, orintegrated into, a microcontroller 302 or other integrated circuits. TheVbus controller 326 may control the voltage output of an adjustable DCsupply 304 which may be used to control power output of the amplifierand power delivered to the resonator coil 344.

The system may comprise sensing and measurement circuitry includingsignal filtering and buffering circuits 318, 320 that may shape, modify,filter, process, buffer, and the like, signals prior to their input toprocessors and/or converters such as analog to digital converters (ADC)314, 316, for example. The processors and converters such as ADCs 314,316 may be integrated into a microcontroller 302 or may be separatecircuits that may be coupled to a processing core 330. Based on measuredsignals, the control algorithm 328 may generate, limit, initiate,extinguish, control, adjust, or modify the operation of any of the PWMgenerator 306, the communication controller 332, the Vbus control 326,the source impedance matching controller 338, the filter/bufferingelements, 318, 320, the converters, 314, 316, the resonator coil 344,and may be part of, or integrated into, a microcontroller 302 or aseparate circuit. The impedance matching networks 342 and resonatorcoils 344 may include electrically controllable, variable, or tunablecomponents such as capacitors, switches, inductors, and the like, asdescribed herein, and these components may have their component valuesor operating points adjusted according to signals received from thesource impedance matching controller 338. Components may be tuned toadjust the operation and characteristics of the resonator including thepower delivered to and by the resonator, the resonant frequency of theresonator, the impedance of the resonator, the Q of the resonator, andany other coupled systems, and the like. The resonator may be any typeor structure resonator described herein including a capacitively loadedloop resonator, a planer resonator comprising a magnetic material or anycombination thereof.

The full bridge system topology depicted in FIG. 4 may comprise aprocessing unit that executes a master control algorithm 328. Theprocessing unit executing the control algorithm 328 may be amicrocontroller, an application specific circuit, a field programmablegate array, a processor, a digital signal processor, and the like. Thesystem may comprise a source/device and/or source/other resonatorcommunication controller 332 coupled to wireless communication circuitry312. The source/device and/or source/other resonator communicationcontroller 332 may be part of the same processing unit that executesthat master control algorithm, it may a part or a circuit within amicrocontroller 302, it may be external to the wireless powertransmission modules, it may be substantially similar to communicationcontrollers used in wire powered or battery powered applications butadapted to include some new or different functionality to enhance orsupport wireless power transmission.

The system may comprise a PWM generator 410 with at least two outputscoupled to at least four transistor gate drivers 334 that may becontrolled by signals generated in a master control algorithm. The fourtransistor gate drivers 334 may be coupled to four power transistors 336directly or via gate drive transformers that may drive the sourceresonator coil 344 through impedance matching networks 342. The powertransistors 336 may be coupled and powered with an adjustable DC supply304 and the adjustable DC supply 304 may be controlled by a Vbuscontroller 326 which may be controlled by a master control algorithm.The Vbus controller 326 may control the voltage output of the adjustableDC supply 304 which may be used to control power output of the amplifierand power delivered to the resonator coil 344.

The system may comprise sensing and measurement circuitry includingsignal filtering and buffering circuits 318, 320 and differential/singleended conversion circuitry 402, 404 that may shape, modify, filter,process, buffer, and the like, signals prior to being input toprocessors and/or converters such as analog to digital converters (ADC)314, 316. The processors and/or converters such as ADC 314, 316 may beintegrated into a microcontroller 302 or may be separate circuits thatmay be coupled to a processing core 330. Based on measured signals, themaster control algorithm may generate, limit, initiate, extinguish,control, adjust, or modify the operation of any of the PWM generator410, the communication controller 332, the Vbus controller 326, thesource impedance matching controller 338, the filter/buffering elements,318, 320, differential/single ended conversion circuitry 402, 404, theconverters, 314, 316, the resonator coil 344, and may be part of orintegrated into a microcontroller 302 or a separate circuit.

Impedance matching networks 342 and resonator coils 344 may compriseelectrically controllable, variable, or tunable components such ascapacitors, switches, inductors, and the like, as described herein, andthese components may have their component values or operating pointsadjusted according to signals received from the source impedancematching controller 338. Components may be tuned to enable tuning of theoperation and characteristics of the resonator including the powerdelivered to and by the resonator, the resonant frequency of theresonator, the impedance of the resonator, the Q of the resonator, andany other coupled systems, and the like. The resonator may be any typeor structure resonator described herein including a capacitively loadedloop resonator, a planar resonator comprising a magnetic material or anycombination thereof.

Impedance matching networks may comprise fixed value components such ascapacitors, inductors, and networks of components as described herein.Parts of the impedance matching networks, A, B and C, may compriseinductors, capacitors, transformers, and series and parallelcombinations of such components, as described herein. In someembodiments, parts of the impedance matching networks A, B, and C, maybe empty (short-circuited). In some embodiments, part B comprises aseries combination of an inductor and a capacitor, and part C is empty.

The full bridge topology may allow operation at higher output powerlevels using the same DC bus voltage as an equivalent half bridgeamplifier. The half bridge exemplary topology of FIG. 3 may provide asingle-ended drive signal, while the exemplary full bridge topology ofFIG. 4 may provide a differential drive to the source resonator 308. Theimpedance matching topologies and components and the resonator structuremay be different for the two systems, as discussed herein.

The exemplary systems depicted in FIGS. 3 and 4 may further includefault detection circuitry 340 that may be used to trigger the shutdownof the microcontroller in the source amplifier or to change or interruptthe operation of the amplifier. This protection circuitry may comprise ahigh speed comparator or comparators to monitor the amplifier returncurrent, the amplifier bus voltage (Vbus) from the DC supply 304, thevoltage across the source resonator 308 and/or the optional tuningboard, or any other voltage or current signals that may cause damage tocomponents in the system or may yield undesirable operating conditions.Preferred embodiments may depend on the potentially undesirableoperating modes associated with different applications. In someembodiments, protection circuitry may not be implemented or circuits maynot be populated. In some embodiments, system and component protectionmay be implemented as part of a master control algorithm and othersystem monitoring and control circuits. In embodiments, dedicated faultcircuitry 340 may include an output (not shown) coupled to a mastercontrol algorithm 328 that may trigger a system shutdown, a reduction ofthe output power (e.g. reduction of Vbus), a change to the PWMgenerator, a change in the operating frequency, a change to a tuningelement, or any other reasonable action that may be implemented by thecontrol algorithm 328 to adjust the operating point mode, improve systemperformance, and/or provide protection.

As described herein, sources in wireless power transfer systems may usea measurement of the input impedance of the impedance matching network342 driving source resonator coil 344 as an error or control signal fora system control loop that may be part of the master control algorithm.In exemplary embodiments, variations in any combination of threeparameters may be used to tune the wireless power source to compensatefor changes in environmental conditions, for changes in coupling, forchanges in device power demand, for changes in module, circuit,component or subsystem performance, for an increase or decrease in thenumber or sources, devices, or repeaters in the system, for userinitiated changes, and the like. In exemplary embodiments, changes tothe amplifier duty cycle, to the component values of the variableelectrical components such as variable capacitors and inductors, and tothe DC bus voltage may be used to change the operating point oroperating range of the wireless source and improve some system operatingvalue. The specifics of the control algorithms employed for differentapplications may vary depending on the desired system performance andbehavior.

Impedance measurement circuitry such as described herein, and shown inFIGS. 3 and 4, may be implemented using two-channel simultaneoussampling ADCs and these ADCs may be integrated into a microcontrollerchip or may be part of a separate circuit. Simultaneously sampling ofthe voltage and current signals at the input to a source resonator'simpedance matching network and/or the source resonator, may yield thephase and magnitude information of the current and voltage signals andmay be processed using known signal processing techniques to yieldcomplex impedance parameters. In some embodiments, monitoring only thevoltage signals or only the current signals may be sufficient.

The impedance measurements described herein may use direct samplingmethods which may be relatively simpler than some other known samplingmethods. In embodiments, measured voltage and current signals may beconditioned, filtered and scaled by filtering/buffering circuitry beforebeing input to ADCs. In embodiments, the filter/buffering circuitry maybe adjustable to work at a variety of signal levels and frequencies, andcircuit parameters such as filter shapes and widths may be adjustedmanually, electronically, automatically, in response to a controlsignal, by the master control algorithm, and the like. Exemplaryembodiments of filter/buffering circuits are shown in FIGS. 3, 4, and 5.

FIG. 5 shows more detailed views of exemplary circuit components thatmay be used in filter/buffering circuitry. In embodiments, and dependingon the types of ADCs used in the system designs, single-ended amplifiertopologies may reduce the complexity of the analog signal measurementpaths used to characterize system, subsystem, module and/or componentperformance by eliminating the need for hardware to convert fromdifferential to single-ended signal formats. In other implementations,differential signal formats may be preferable. The implementations shownin FIG. 5 are exemplary, and should not be construed to be the onlypossible way to implement the functionality described herein. Rather itshould be understood that the analog signal path may employ componentswith different input requirements and hence may have different signalpath architectures.

In both the single ended and differential amplifier topologies, theinput current to the impedance matching networks 342 driving theresonator coils 344 may be obtained by measuring the voltage across acapacitor 324, or via a current sensor of some type. For the exemplarysingle-ended amplifier topology in FIG. 3, the current may be sensed onthe ground return path from the impedance matching network 342. For theexemplary differential power amplifier depicted in FIG. 4, the inputcurrent to the impedance matching networks 342 driving the resonatorcoils 344 may be measured using a differential amplifier across theterminals of a capacitor 324 or via a current sensor of some type. Inthe differential topology of FIG. 4, the capacitor 324 may be duplicatedat the negative output terminal of the source power amplifier.

In both topologies, after single ended signals representing the inputvoltage and current to the source resonator and impedance matchingnetwork are obtained, the signals may be filtered 502 to obtain thedesired portions of the signal waveforms. In embodiments, the signalsmay be filtered to obtain the fundamental component of the signals. Inembodiments, the type of filtering performed, such as low pass,bandpass, notch, and the like, as well as the filter topology used, suchas elliptical, Chebyshev, Butterworth, and the like, may depend on thespecific requirements of the system. In some embodiments, no filteringwill be required.

The voltage and current signals may be amplified by an optionalamplifier 504. The gain of the optional amplifier 504 may be fixed orvariable. The gain of the amplifier may be controlled manually,electronically, automatically, in response to a control signal, and thelike. The gain of the amplifier may be adjusted in a feedback loop, inresponse to a control algorithm, by the master control algorithm, andthe like. In embodiments, required performance specifications for theamplifier may depend on signal strength and desired measurementaccuracy, and may be different for different application scenarios andcontrol algorithms.

The measured analog signals may have a DC offset added to them, 506,which may be required to bring the signals into the input voltage rangeof the ADC which for some systems may be 0 to 3.3V. In some systems thisstage may not be required, depending on the specifications of theparticular ADC used.

As described above, the efficiency of power transmission between a powergenerator and a power load may be impacted by how closely matched theoutput impedance of the generator is to the input impedance of the load.In an exemplary system as shown in FIG. 6A, power may be delivered tothe load at a maximum possible efficiency, when the input impedance ofthe load 604 is equal to the complex conjugate of the internal impedanceof the power generator or the power amplifier 602. Designing thegenerator or load impedance to obtain a high and/or maximum powertransmission efficiency may be called “impedance matching”. Impedancematching may be performed by inserting appropriate networks or sets ofelements such as capacitors, resistors, inductors, transformers,switches and the like, to form an impedance matching network 606,between a power generator 602 and a power load 604 as shown in FIG. 6B.In other embodiments, mechanical adjustments and changes in elementpositioning may be used to achieve impedance matching. As describedabove for varying loads, the impedance matching network 606 may includevariable components that are dynamically adjusted to ensure that theimpedance at the generator terminals looking towards the load and thecharacteristic impedance of the generator remain substantially complexconjugates of each other, even in dynamic environments and operatingscenarios. In embodiments, dynamic impedance matching may beaccomplished by tuning the duty cycle, and/or the phase, and/or thefrequency of the driving signal of the power generator or by tuning aphysical component within the power generator, such as a capacitor, asdepicted in FIG. 6C. Such a tuning mechanism may be advantageous becauseit may allow impedance matching between a power generator 608 and a loadwithout the use of a tunable impedance matching network, or with asimplified tunable impedance matching network 606, such as one that hasfewer tunable components for example. In embodiments, tuning the dutycycle, and/or frequency, and/or phase of the driving signal to a powergenerator may yield a dynamic impedance matching system with an extendedtuning range or precision, with higher power, voltage and/or currentcapabilities, with faster electronic control, with fewer externalcomponents, and the like. The impedance matching methods, architectures,algorithms, protocols, circuits, measurements, controls, and the like,described below, may be useful in systems where power generators drivehigh-Q magnetic resonators and in high-Q wireless power transmissionsystems as described herein. In wireless power transfer systems a powergenerator may be a power amplifier driving a resonator, sometimesreferred to as a source resonator, which may be a load to the poweramplifier. In wireless power applications, it may be preferable tocontrol the impedance matching between a power amplifier and a resonatorload to control the efficiency of the power delivery from the poweramplifier to the resonator. The impedance matching may be accomplished,or accomplished in part, by tuning or adjusting the duty cycle, and/orthe phase, and/or the frequency of the driving signal of the poweramplifier that drives the resonator.

Efficiency of Switching Amplifiers

Switching amplifiers, such as class D, E, F amplifiers, and the like orany combinations thereof, deliver power to a load at a maximumefficiency when no power is dissipated on the switching elements of theamplifier. This operating condition may be accomplished by designing thesystem so that the switching operations which are most critical (namelythose that are most likely to lead to switching losses) are done whenboth the voltage across the switching element and the current throughthe switching element are zero. These conditions may be referred to asZero Voltage Switching (ZVS) and Zero Current Switching (ZCS) conditionsrespectively. When an amplifier operates at ZVS and ZCS either thevoltage across the switching element or the current through theswitching element is zero and thus no power can be dissipated in theswitch. Since a switching amplifier may convert DC (or very lowfrequency AC) power to AC power at a specific frequency or range offrequencies, a filter may be introduced before the load to preventunwanted harmonics that may be generated by the switching process fromreaching the load and being dissipated there. In embodiments, aswitching amplifier may be designed to operate at maximum efficiency ofpower conversion, when connected to a resonant load, with a nontrivialquality factor (say Q>5), and of a specificimpedanceZ*_(o)=R_(o)+jX_(o), which leads to simultaneous ZVS and ZCS.We define Z_(o)=R_(o)−jX_(o) as the characteristic impedance of theamplifier, so that achieving maximum power transmission efficiency isequivalent to impedance matching the resonant load to the characteristicimpedance of the amplifier.

In a switching amplifier, the switching frequency of the switchingelements, f_(switch), wherein f_(switch)=ω/2π and the duty cycle, dc, ofthe ON switch-state duration of the switching elements may be the samefor all switching elements of the amplifier. In this specification, wewill use the term “class D” to denote both class D and class DEamplifiers, that is, switching amplifiers with dc<=50%.

The value of the characteristic impedance of the amplifier may depend onthe operating frequency, the amplifier topology, and the switchingsequence of the switching elements. In some embodiments, the switchingamplifier may be a half-bridge topology and, in some embodiments, afull-bridge topology. In some embodiments, the switching amplifier maybe class D and, in some embodiments, class E. In any of the aboveembodiments, assuming the elements of the bridge are symmetric, thecharacteristic impedance of the switching amplifier has the formR _(o) =F _(R)(dc)ωC _(a) ,X _(o) =F _(X)(dc)/ωC _(a),  (1)where dc is the duty cycle of ON switch-state of the switching elements,the functions F_(R)(dc) and F_(X)(dc) are plotted in FIG. 7 (both forclass D and E), (t) is the frequency at which the switching elements areswitched, and C_(a)=n_(a)C_(switc┘) where C_(switc┘) is the capacitanceacross each switch, including both the transistor output capacitance andalso possible external capacitors placed in parallel with the switch,while n_(a)=1 for a full bridge and n_(a)=2 for a half bridge. For classD, one can also write the analytical expressionsF _(R)(dc)=sin² u/π,F _(X)(dc)=(u−sin u*cos u)/π,  (2)where u=π(1−2*dc), indicating that the characteristic impedance level ofa class D amplifier decreases as the duty cycle, dc, increases towards50%. For a class D amplifier operation with dc=50%, achieving ZVS andZCS is possible only when the switching elements have practically nooutput capacitance (C_(a)=0) and the load is exactly on resonance(X₀=0), while R_(o) can be arbitrary.

Impedance Matching Networks

In applications, the driven load may have impedance that is verydifferent from the characteristic impedance of the external drivingcircuit, to which it is connected. Furthermore, the driven load may notbe a resonant network. An Impedance Matching Network (IMN) is a circuitnetwork that may be connected before a load as in FIG. 6B, in order toregulate the impedance that is seen at the input of the networkconsisting of the IMN circuit and the load. An IMN circuit may typicallyachieve this regulation by creating a resonance close to the drivingfrequency. Since such an IMN circuit accomplishes all conditions neededto maximize the power transmission efficiency from the generator to theload (resonance and impedance matching—ZVS and ZCS for a switchingamplifier), in embodiments, an IMN circuit may be used between thedriving circuit and the load.

For an arrangement shown in FIG. 6B, let the input impedance of thenetwork consisting of the Impedance Matching Network (IMN) circuit andthe load (denoted together from now on as IMN+load) beZ_(l)=R_(l)(ω)+jX_(l)(ω). The impedance matching conditions of thisnetwork to the external circuit with characteristic impedanceZ_(o)=R_(o)−jX_(o) are then R_(l)(ω)=R_(o), X_(l)(ω)=X_(o).

Methods for Tunable Impedance Matching of a Variable Load

In embodiments where the load may be variable, impedance matchingbetween the load and the external driving circuit, such as a linear orswitching power amplifier, may be achieved by using adjustable/tunablecomponents in the IMN circuit that may be adjusted to match the varyingload to the fixed characteristic impedance Z_(o) of the external circuit(FIG. 6B). To match both the real and imaginary parts of the impedancetwo tunable/variable elements in the IMN circuit may be needed.

In embodiments, the load may be inductive (such as a resonator coil)with impedance R+jωL, so the two tunable elements in the IMN circuit maybe two tunable capacitance networks or one tunable capacitance networkand one tunable inductance network or one tunable capacitance networkand one tunable mutual inductance network.

In embodiments where the load may be variable, the impedance matchingbetween the load and the driving circuit, such as a linear or switchingpower amplifier, may be achieved by using adjustable/tunable componentsor parameters in the amplifier circuit that may be adjusted to match thecharacteristic impedance Z_(o) of the amplifier to the varying (due toload variations) input impedance of the network consisting of the IMNcircuit and the load (IMN+load), where the IMN circuit may also betunable (FIG. 6C). To match both the real and imaginary parts of theimpedance, a total of two tunable/variable elements or parameters in theamplifier and the IMN circuit may be needed. The disclosed impedancematching method can reduce the required number of tunable/variableelements in the IMN circuit or even completely eliminate the requirementfor tunable/variable elements in the IMN circuit. In some examples, onetunable element in the power amplifier and one tunable element in theIMN circuit may be used. In some examples, two tunable elements in thepower amplifier and no tunable element in the IMN circuit may be used.

In embodiments, the tunable elements or parameters in the poweramplifier may be the frequency, amplitude, phase, waveform, duty cycleand the like of the drive signals applied to transistors, switches,diodes and the like.

In embodiments, the power amplifier with tunable characteristicimpedance may be a tunable switching amplifier of class D, E, F or anycombinations thereof. Combining Equations (1) and (2), the impedancematching conditions for this network areR _(l)(ω)=F _(R)(dC)/ωC _(a) ,X _(l)(ω)=F _(x)(dC)/ωC _(a)  (3).

In some examples of a tunable switching amplifier, one tunable elementmay be the capacitance C_(a), which may be tuned by tuning the externalcapacitors placed in parallel with the switching elements.

In some examples of a tunable switching amplifier, one tunable elementmay be the duty cycle dc of the ON switch-state of the switchingelements of the amplifier. Adjusting the duty cycle, dc, via Pulse WidthModulation (PWM) has been used in switching amplifiers to achieve outputpower control. In this specification, we disclose that PWM may also beused to achieve impedance matching, namely to satisfy Eqs.(3), and thusmaximize the amplifier efficiency.

In some examples of a tunable switching amplifier one tunable elementmay be the switching frequency, which is also the driving frequency ofthe IMN+load network and may be designed to be substantially close tothe resonant frequency of the IMN+load network. Tuning the switchingfrequency may change the characteristic impedance of the amplifier andthe impedance of the IMN+load network. The switching frequency of theamplifier may be tuned appropriately together with one more tunableparameters, so that Eqs.(3) are satisfied.

A benefit of tuning the duty cycle and/or the driving frequency of theamplifier for dynamic impedance matching is that these parameters can betuned electronically, quickly, and over a broad range. In contrast, forexample, a tunable capacitor that can sustain a large voltage and has alarge enough tunable range and quality factor may be expensive, slow orunavailable for with the necessary component specifications

Examples of Methods for Tunable Impedance Matching of a Variable Load

A simplified circuit diagram showing the circuit level structure of aclass D power amplifier 802, impedance matching network 804 and aninductive load 806 is shown in FIG. 8. The diagram shows the basiccomponents of the system with the switching amplifier 804 comprising apower source 810, switching elements 808, and capacitors. The impedancematching network 804 comprising inductors and capacitors, and the load806 modeled as an inductor and a resistor.

An exemplary embodiment of this inventive tuning scheme comprises ahalf-bridge class-D amplifier operating at switching frequency f anddriving a low-loss inductive element R+jωL via an IMN, as shown in FIG.8.

In some embodiments L′ may be tunable. L′ may be tuned by a variabletapping point on the inductor or by connecting a tunable capacitor inseries or in parallel to the inductor. In some embodiments C_(a) may betunable. For the half bridge topology, C_(a) may be tuned by varyingeither one or both capacitors C_(switc┘), as only the parallel sum ofthese capacitors matters for the amplifier operation. For the fullbridge topology, C_(a) may be tuned by varying either one, two, three orall capacitors C_(switc┘), as only their combination (series sum of thetwo parallel sums associated with the two halves of the bridge) mattersfor the amplifier operation.

In some embodiments of tunable impedance matching, two of the componentsof the IMN may be tunable. In some embodiments, L′ and C₂ may be tuned.Then, FIG. 9 shows the values of the two tunable components needed toachieve impedance matching as functions of the varying R and L of theinductive element, and the associated variation of the output power (atgiven DC bus voltage) of the amplifier, for f=250 kHz, dc=40%, C_(a)=640pF and C₁=10 nF. Since the IMN always adjusts to the fixedcharacteristic impedance of the amplifier, the output power is alwaysconstant as the inductive element is varying.

In some embodiments of tunable impedance matching, elements in theswitching amplifier may also be tunable. In some embodiments thecapacitance C_(a) along with the IMN capacitor C₂ may be tuned. Then,FIG. 10 shows the values of the two tunable components needed to achieveimpedance matching as functions of the varying R and L of the inductiveelement, and the associated variation of the output power (at given DCbus voltage) of the amplifier for f=250 kHz, dc=40%, C₁=10 nF andωL′=1000Ω. It can be inferred from FIG. 10 that C₂ needs to be tunedmainly in response to variations in L and that the output powerdecreases as R increases.

In some embodiments of tunable impedance matching, the duty cycle dcalong with the IMN capacitor C₂ may be tuned. Then, FIG. 11 shows thevalues of the two tunable parameters needed to achieve impedancematching as functions of the varying R and L of the inductive element,and the associated variation of the output power (at given DC busvoltage) of the amplifier for f=250 kHz, C_(a)=640 pF, C₁=10 nF andωL′=1000Ω. It can be inferred from FIG. 11 that C₂ needs to be tunedmainly in response to variations in L and that the output powerdecreases as R increases.

In some embodiments of tunable impedance matching, the capacitance C_(a)along with the IMN inductor L′ may be tuned. Then, FIG. 11A shows thevalues of the two tunable components needed to achieve impedancematching as functions of the varying R of the inductive element, and theassociated variation of the output power (at given DC bus voltage) ofthe amplifier for f=250 kHz, dc=40%, C₁=10 nF and C₂=7.5 nF. It can beinferred from FIG. 11A that the output power decreases as R increases.

In some embodiments of tunable impedance matching, the duty cycle dcalong with the IMN inductor L′ may be tuned. Then, FIG. 11B shows thevalues of the two tunable parameters needed to achieve impedancematching as functions of the varying R of the inductive element, and theassociated variation of the output power (at given DC bus voltage) ofthe amplifier for f=250 kHz, C_(a)=640 pF, C₁=10 nF and C₂=7.5 nF asfunctions of the varying R of the inductive element. It can be inferredfrom FIG. 11B that the output power decreases as R increases.

In some embodiments of tunable impedance matching, only elements in theswitching amplifier may be tunable with no tunable elements in the IMN.In some embodiments the duty cycle dc along with the capacitance C_(a)may be tuned. Then, FIG. 11C, shows the values of the two tunableparameters needed to achieve impedance matching as functions of thevarying R of the inductive element, and the associated variation of theoutput power (at given DC bus voltage) of the amplifier for f=250 kHz,C₁=10 nF, C₂=7.5 nF and ωL′=1000Ω. It can be inferred from FIG. 11C thatthe output power is a non-monotonic function of R. These embodiments maybe able to achieve dynamic impedance matching when variations in L (andthus the resonant frequency) are modest.

In some embodiments, dynamic impedance matching with fixed elementsinside the IMN, also when L is varying greatly as explained earlier, maybe achieved by varying the driving frequency of the external frequency f(e.g. the switching frequency of a switching amplifier) so that itfollows the varying resonant frequency of the resonator. Using theswitching frequency f and the switch duty cycle dc as the two variableparameters, full impedance matching can be achieved as R and L arevarying without the need of any variable components. Then, FIG. 12 showsthe values of the two tunable parameters needed to achieve impedancematching as functions of the varying R and L of the inductive element,and the associated variation of the output power (at given DC busvoltage) of the amplifier for C_(a)=640 pF, C₁=10 nF, C₂=7.5 nF andL′=637 μH. It can be inferred from FIG. 12 that the frequency f needs tobe tuned mainly in response to variations in L, as explained earlier.

Tunable Impedance Matching for Systems of Wireless Power Transmission

In applications of wireless power transfer the low-loss inductiveelement may be the coil of a source resonator coupled to one or moredevice resonators or other resonators, such as repeater resonators, forexample. The impedance of the inductive element R+jωL may include thereflected impedances of the other resonators on the coil of the sourceresonator. Variations of R and L of the inductive element may occur dueto external perturbations in the vicinity of the source resonator and/orthe other resonators or thermal drift of components. Variations of R andL of the inductive element may also occur during normal use of thewireless power transmission system due to relative motion of the devicesand other resonators with respect to the source. The relative motion ofthese devices and other resonators with respect to the source, orrelative motion or position of other sources, may lead to varyingcoupling (and thus varying reflected impedances) of the devices to thesource. Furthermore, variations of R and L of the inductive element mayalso occur during normal use of the wireless power transmission systemdue to changes within the other coupled resonators, such as changes inthe power draw of their loads. All the methods and embodiments disclosedso far apply also to this case in order to achieve dynamic impedancematching of this inductive element to the external circuit driving it.

To demonstrate the presently disclosed dynamic impedance matchingmethods for a wireless power transmission system, consider a sourceresonator including a low-loss source coil, which is inductively coupledto the device coil of a device resonator driving a resistive load.

In some embodiments, dynamic impedance matching may be achieved at thesource circuit. In some embodiments, dynamic impedance matching may alsobe achieved at the device circuit. When full impedance matching isobtained (both at the source and the device), the effective resistanceof the source inductive element (namely the resistance of the sourcecoil R_(s) plus the reflected impedance from the device) isR=R_(s)√{square root over (1+U_(sd) ²)}. (Similarly the effectiveresistance of the device inductive element is R_(d)√{square root over(1+U_(sd) ²)}, where R_(d) is the resistance of the device coil.)Dynamic variation of the mutual inductance between the coils due tomotion results in a dynamic variation of U_(sd)=ωM_(sd)/√{square rootover (R_(s)R_(d))}. Therefore, when both source and device aredynamically tuned, the variation of mutual inductance is seen from thesource circuit side as a variation in the source inductive elementresistance R. Note that in this type of variation, the resonantfrequencies of the resonators may not change substantially, since L maynot be changing. Therefore, all the methods and examples presented fordynamic impedance matching may be used for the source circuit of thewireless power transmission system.

Note that, since the resistance R represents both the source coil andthe reflected impedances of the device coils to the source coil, inFIGS. 9-12, as R increases due to the increasing U, the associatedwireless power transmission efficiency increases. In some embodiments,an approximately constant power may be required at the load driven bythe device circuitry. To achieve a constant level of power transmittedto the device, the required output power of the source circuit may needto decrease as U increases. If dynamic impedance matching is achievedvia tuning some of the amplifier parameters, the output power of theamplifier may vary accordingly. In some embodiments, the automaticvariation of the output power is preferred to be monotonicallydecreasing with R, so that it matches the constant device powerrequirement. In embodiments where the output power level is accomplishedby adjusting the DC driving voltage of the power generator, using animpedance matching set of tunable parameters which leads tomonotonically decreasing output power vs. R will imply that constantpower can be kept at the power load in the device with only a moderateadjustment of the DC driving voltage. In embodiments, where the “knob”to adjust the output power level is the duty cycle dc or the phase of aswitching amplifier or a component inside an Impedance Matching Network,using an impedance matching set of tunable parameters which leads tomonotonically decreasing output power vs. R will imply that constantpower can be kept at the power load in the device with only a moderateadjustment of this power “knob”.

In the examples of FIGS. 9-12, if R_(s)=0.19Ω, then the range R=0.2−2Ωcorresponds approximately to U_(sd)=0.3−10.5. For these values, in FIG.14, we show with dashed lines the output power (normalized to DC voltagesquared) required to keep a constant power level at the load, when bothsource and device are dynamically impedance matched. The similar trendbetween the solid and dashed lines explains why a set of tunableparameters with such a variation of output power may be preferable.

In some embodiments, dynamic impedance matching may be achieved at thesource circuit, but impedance matching may not be achieved or may onlypartially be achieved at the device circuit. As the mutual inductancebetween the source and device coils varies, the varying reflectedimpedance of the device to the source may result in a variation of boththe effective resistance R and the effective inductance L of the sourceinductive element. The methods presented so far for dynamic impedancematching are applicable and can be used for the tunable source circuitof the wireless power transmission system.

As an example, consider the circuit of FIG. 14, where f=250 kHz,C_(a)=640 pF, R_(s)=0.19Ω, L_(s)=100 μH, C_(1s)=10 nF, ωL′_(s)=1000Ω,R_(d)=0.3Ω, L_(d)=40 μH, C_(1d)=87.5 nF, C_(2d)=13 nF, ωL′_(d)=400Ω andZ_(l)=50Ω, where s and d denote the source and device resonatorsrespectively and the system is matched at U_(sd)=3. Tuning the dutycycle dc of the switching amplifier and the capacitor C_(2s) may be usedto dynamically impedance match the source, as the non-tunable device ismoving relatively to the source changing the mutual inductance M betweenthe source and the device. In FIG. 14, we show the required values ofthe tunable parameters along with the output power per DC voltage of theamplifier. The dashed line again indicates the output power of theamplifier that would be needed so that the power at the load is aconstant value.

In some embodiments, tuning the driving frequency f of the sourcedriving circuit may still be used to achieve dynamic impedance matchingat the source for a system of wireless power transmission between thesource and one or more devices. As explained earlier, this methodenables full dynamic impedance matching of the source, even when thereare variations in the source inductance L_(s) and thus the sourceresonant frequency. For efficient power transmission from the source tothe devices, the device resonant frequencies must be tuned to follow thevariations of the matched driving and source-resonant frequencies.Tuning a device capacitance (for example, in the embodiment of FIG. 13C_(1d) or C_(2d)) may be necessary, when there are variations in theresonant frequency of either the source or the device resonators. Infact, in a wireless power transfer system with multiple sources anddevices, tuning the driving frequency alleviates the need to tune onlyone source-object resonant frequency, however, all the rest of theobjects may need a mechanism (such as a tunable capacitance) to tunetheir resonant frequencies to match the driving frequency.

Resonator Thermal Management

In wireless energy transfer systems, some portion of the energy lostduring the wireless transfer process is dissipated as heat. Energy maybe dissipated in the resonator components themselves. For example, evenhigh-Q conductors and components have some loss or resistance, and theseconductors and components may heat up when electric currents and/orelectromagnetic fields flow through them. Energy may be dissipated inmaterials and objects around a resonator. For example, eddy currentsdissipated in imperfect conductors or dielectrics surrounding or near-bythe resonator may heat up those objects. In addition to affecting thematerial properties of those objects, this heat may be transferredthrough conductive, radiative, or convective processes to the resonatorcomponents. Any of these heating effects may affect the resonator Q,impedance, frequency, etc., and therefore the performance of thewireless energy transfer system.

In a resonator comprising a block or core of magnetic material, heat maybe generated in the magnetic material due to hysteresis losses and toresistive losses resulting from induced eddy currents. Both effectsdepend on the magnetic flux density in the material, and both can createsignificant amounts of heat, especially in regions where the fluxdensity or eddy currents may be concentrated or localized. In additionto the flux density, the frequency of the oscillating magnetic field,the magnetic material composition and losses, and the ambient oroperating temperature of the magnetic material may all impact howhysteresis and resistive losses heat the material.

In embodiments, the properties of the magnetic material such as the typeof material, the dimensions of the block, and the like, and the magneticfield parameters may be chosen for specific operating power levels andenvironments to minimize heating of the magnetic material. In someembodiments, changes, cracks, or imperfections in a block of magneticmaterial may increase the losses and heating of the magnetic material inwireless power transmission applications.

For magnetic blocks with imperfections, or that are comprised of smallersize tiles or pieces of magnetic material arranged into a larger unit,the losses in the block may be uneven and may be concentrated in regionswhere there are inhomogeneities or relatively narrow gaps betweenadjacent tiles or pieces of magnetic material. For example, if anirregular gap exists in a magnetic block of material, then the effectivereluctance of various magnetic flux paths through the material may besubstantially irregular and the magnetic field may be more concentratedin portions of the block where the magnetic reluctance is lowest. Insome cases, the effective reluctance may be lowest where the gap betweentiles or pieces is narrowest or where the density of imperfections islowest. Because the magnetic material guides the magnetic field, themagnetic flux density may not be substantially uniform across the block,but may be concentrated in regions offering relatively lower reluctance.Irregular concentrations of the magnetic field within a block ofmagnetic material may not be desirable because they may result in unevenlosses and heat dissipation in the material.

For example, consider a magnetic resonator comprising a conductor 1506wrapped around a block of magnetic material composed of two individualtiles 1502, 1504 of magnetic material joined such that they form a seam1508 that is perpendicular to the axis of the conductor 1506 loops asdepicted in FIG. 15. An irregular gap in the seam 1508 between the tilesof magnetic material 1502, 1504 may force the magnetic field 1512(represented schematically by the dashed magnetic field lines) in theresonator to concentrate in a sub region 1510 of the cross section ofthe magnetic material. Since the magnetic field will follow the path ofleast reluctance, a path including an air gap between two pieces ofmagnetic material may create an effectively higher reluctance path thanone that traverses the width of the magnetic material at a point wherethe pieces of magnetic materials touch or have a smaller air gap. Themagnetic flux density may therefore preferentially flow through arelatively small cross area of the magnetic material resulting in a highconcentration of magnetic flux in that small area 1510.

In many magnetic materials of interest, more inhomogeneous flux densitydistributions lead to higher overall losses. Moreover, the moreinhomogeneous flux distribution may result in material saturation andcause localized heating of the area in which the magnetic flux isconcentrated. The localized heating may alter the properties of themagnetic material, in some cases exacerbating the losses. For example,in the relevant regimes of operation of some materials, hysteresis andresistive losses increase with temperature. If heating the materialincreases material losses, resulting in more heating, the temperature ofthe material may continue to increase and even runaway if no correctiveaction is taken. In some instances, the temperature may reach 100 C ormore and may degrade the properties of the magnetic material and theperformance of wireless power transfer. In some instances, the magneticmaterials may be damaged, or the surrounding electronic components,packaging and/or enclosures may be damaged by the excessive heat.

In embodiments, variations or irregularities between tiles or pieces ofthe block of magnetic material may be minimized by machining, polishing,grinding, and the like, the edges of the tiles or pieces to ensure atight fit between tiles of magnetic materials providing a substantiallymore uniform reluctance through the whole cross section of the block ofmagnetic material. In embodiments, a block of magnetic material mayrequire a means for providing a compression force between the tiles toensure the tiles are pressed tight together without gaps. Inembodiments, an adhesive may be used between the tiles to ensure theyremain in tight contact.

In embodiments the irregular spacing of adjacent tiles of magneticmaterial may be reduced by adding a deliberate gap between adjacenttiles of magnetic material. In embodiments a deliberate gap may be usedas a spacer to ensure even or regular separations between magneticmaterial tiles or pieces. Deliberate gaps of flexible materials may alsoreduce irregularities in the spacings due to tile movement orvibrations. In embodiments, the edges of adjacent tiles of magneticmaterial may be taped, dipped, coated, and the like with an electricalinsulator, to prevent eddy currents from flowing through reducedcross-sectional areas of the block, thus lowering the eddy currentlosses in the material. In embodiments a separator may be integratedinto the resonator packaging. The spacer may provide a spacing of 1 mmor less.

In embodiments, the mechanical properties of the spacer between tilesmay be chosen so as to improve the tolerance of the overall structure tomechanical effects such as changes in the dimensions and/or shape of thetiles due to intrinsic effects (e.g., magnetostriction, thermalexpansion, and the like) as well as external shocks and vibrations. Forexample, the spacer may have a desired amount of mechanical give toaccommodate the expansion and/or contraction of individual tiles, andmay help reduce the stress on the tiles when they are subjected tomechanical vibrations, thus helping to reduce the appearance of cracksand other defects in the magnetic material.

In embodiments, it may be preferable to arrange the individual tilesthat comprise the block of magnetic material to minimize the number ofseams or gaps between tiles that are perpendicular to the dipole momentof the resonator. In embodiments it may be preferable to arrange andorient the tiles of magnetic material to minimize the gaps between tilesthat are perpendicular to the axis formed by the loops of a conductorcomprising the resonator.

For example, consider the resonator structure depicted in FIG. 16. Theresonator comprises a conductor 1604 wrapped around a block of magneticmaterial comprising six separate individual tiles 1602 arranged in athree by two array. The arrangement of tiles results in two tile seams1606, 1608 when traversing the block of magnetic material in onedirection, and only one tile seam 1610 when traversing the block ofmagnetic material in the orthogonal direction. In embodiments, it may bepreferable to wrap the conductor wire 1604 around the block of magneticmaterial such that the dipole moment of the resonator is perpendicularto the fewest number of tile seams. The inventors have observed thatthere is relatively less heating induced around seams and gaps 1606,1608 that are parallel to the dipole moment of the resonator. Seams andgaps that run perpendicular to the dipole moment of the resonator mayalso be referred to as critical seams or critical seam areas. It maystill be desirable, however, to electrically insulate gaps that runparallel to the dipole moment of the resonator (such as 1606 and 1608)so as to reduce eddy current losses. Uneven contact between tilesseparated by such parallel gaps may cause eddy currents to flow throughnarrow contact points, leading to large losses at such points.

In embodiments, irregularities in spacing may be tolerated with adequatecooling of the critical seam areas to prevent the localized degradationof material properties when the magnetic material heats up. Maintainingthe temperature of the magnetic material below a critical temperaturemay prevent a runaway effect caused by a sufficiently high temperature.With proper cooling of the critical seam area, the wireless energytransfer performance may be satisfactory despite the additional loss andheating effects due to irregular spacing, cracks, or gaps between tiles.

Effective heatsinking of the resonator structure to prevent excessivelocalized heating of the magnetic material poses several challenges.Metallic materials that are typically used for heatsinks and thermalconduction can interact with the magnetic fields used for wirelessenergy transfer by the resonators and affect the performance of thesystem. Their location, size, orientation, and use should be designed soas to not excessively lower the perturbed Q of the resonators in thepresence of these heatsinking materials. In addition, owing to therelatively poor thermal conductivity of magnetic materials such asferrites, a relatively large contact area between the heatsink and themagnetic material may be required to provide adequate cooling which mayrequire placement of substantial amount of lossy materials close to themagnetic resonator.

In embodiments, adequate cooling of the resonator may be achieved withminimal effect on the wireless energy transfer performance withstrategic placement of thermally conductive materials. In embodiments,strips of thermally conductive material may be placed in between loopsof conductor wire and in thermal contact with the block of magneticmaterial.

One exemplary embodiment of a resonator with strips of thermallyconductive material is depicted in FIG. 17. FIG. 17A shows the resonatorstructure without the conducting strips and with the block of magneticmaterial comprising smaller tiles of magnetic material forming gaps orseams. Strips of thermally conductive 1708 material may be placed inbetween the loops of the conductor 1702 and in thermal contact with theblock of magnetic material 1704 as depicted in FIGS. 17B and 17C. Tominimize the effects of the strips on the parameters of the resonator,in some embodiments it may be preferable to arrange the strips parallelto the loops of conductor or perpendicular to the dipole moment of theresonator. The strips of conductor may be placed to cover as much or asmany of the seams or gaps between the tiles as possible especially theseams between tiles that are perpendicular to the dipole moment of theresonator.

In embodiments the thermally conductive material may comprise copper,aluminum, brass, thermal epoxy, paste, pads, and the like, and may beany material that has a thermal conductivity that is at least that ofthe magnetic material in the resonator (˜5 W/(K-m) for some commercialferrite materials). In embodiments where the thermally conductivematerial is also electrically conducting, the material may require alayer or coating of an electrical insulator to prevent shorting anddirect electrical contact with the magnetic material or the loops ofconductor of the resonator.

In embodiments the strips of thermally conductive material may be usedto conduct heat from the resonator structure to a structure or mediumthat can safely dissipate the thermal energy. In embodiments thethermally conductive strips may be connected to a heat sink such as alarge plate located above the strips of conductor that can dissipate thethermal energy using passive or forced convection, radiation, orconduction to the environment. In embodiments the system may include anynumber of active cooling systems that may be external or internal to theresonator structure that can dissipate the thermal energy from thethermally conducting strips and may include liquid cooling systems,forced air systems, and the like. For example, the thermally conductingstrips may be hollow or comprise channels for coolant that may be pumpedor forced through to cool the magnetic material. In embodiments, a fielddeflector made of a good electrical conductor (such as copper, silver,aluminum, and the like) may double as part of the heatsinking apparatus.The addition of thermally and electrically conducting strips to thespace between the magnetic material and the field deflector may have amarginal effect on the perturbed Q, as the the electromagnetic fields inthat space are typically suppressed by the presence of the fielddeflector. Such conducting strips may be thermally connected to both themagnetic material and the field deflector to make the temperaturedistribution among different strips more homogeneous.

In embodiments the thermally conducting strips are spaced to allow atleast one loop of conductor to wrap around the magnetic material. Inembodiments the strips of thermally conductive material may bepositioned only at the gaps or seams of the magnetic material. In otherembodiments, the strips may be positioned to contact the magneticmaterial at substantially throughout its complete length. In otherembodiments, the strips may be distributed to match the flux densitywithin the magnetic material. Areas of the magnetic material which undernormal operation of the resonator may have higher magnetic fluxdensities may have a higher density of contact with the thermallyconductive strips. In embodiments depicted in FIG. 17A) for example, thehighest magnetic flux density in the magnetic material may be observedtoward the center of the block of magnetic material and the lowerdensity may be toward the ends of the block in the direction of thedipole moment of the resonator.

To show how the use of thermally conducting strips helps to reduce theoverall temperature in the magnetic material as well as the temperatureat potential hot spots, the inventors have performed a finite elementsimulation of a resonator structure similar to that depicted in FIG.17C. The structure was simulated operating at a frequency of 235 kHz andcomprising a block of EPCOS N95 magnetic material measuring 30 cm×30cm×5 mm excited by 10 turns of litz wire (symmetrically placed at 25 mm,40 mm, 55 mm, 90 mm and 105 mm from the plane of symmetry of thestructure) carrying 40 A of peak current each, and thermally connectedto a 50 cm×50 cm×4 mm field deflector by means of three 3×¾×1′ hollowsquare tubes (⅛″ wall thickness) of aluminum (alloy 6063) whose centralaxes are placed at −75 mm, 0 mm, and +75 from the symmetry plane of thestructure. The perturbed Q due to the field deflector and hollow tubeswas found to be 1400 (compared to 1710 for the same structure withoutthe hollow tubes). The power dissipated in the shield and tubes wascalculated to be 35.6 W, while that dissipated in the magnetic materialwas 58.3 W. Assuming the structure is cooled by air convection andradiation and an ambient temperature of 24° C., the maximum temperaturein the structure was 85° C. (at points in the magnetic materialapproximately halfway between the hollow tubes) while the temperature inparts of the magnetic material in contact with the hollow tubes wasapproximately 68° C. By comparison, the same resonator without thethermally conducting hollow tubes dissipated 62.0 W in the magneticmaterial for the same excitation current of 40 W peak and the maximumtemperature in the magnetic material was found to be 111° C.

The advantage of the conducting strips is more apparent still if weintroduce a defect in a portion of the magnetic material that is in goodthermal contact with the tubes. An air gap 10 cm long and 0.5 mm placedat the center of the magnetic material and oriented perpendicular to thedipole moment increases the power dissipated in the magnetic material to69.9 W (the additional 11.6 W relative to the previously discussedno-defect example being highly concentrated in the vicinity of the gap),but the conducting tube ensures that the maximum temperature in themagnetic material has only a relative modest increase of 11° C. to 96°C. In contrast, the same defect without the conducting tubes leads to amaximum temperature of 161° C. near the defect. Cooling solutions otherthan convection and radiation, such as thermally connecting theconducting tubes body with large thermal mass or actively cooling them,may lead to even lower operational temperatures for this resonator atthe same current level.

In embodiments thermally conductive strips of material may be positionedat areas that may have the highest probability of developing cracks thatmay cause irregular gaps in the magnetic material. Such areas may beareas of high stress or strain on the material, or areas with poorsupport or backing from the packaging of the resonator. Strategicallypositioned thermally conductive strips may ensure that as cracks orirregular gaps develop in the magnetic material, the temperature of themagnetic material will be maintained below its critical temperature. Thecritical temperature may be defined as the Curie temperature of themagnetic material, or any temperature at which the characteristics ofthe resonator have been degraded beyond the desired performanceparameters.

In embodiments the heastsinking structure may provide mechanical supportto the magnetic material. In embodiments the heatsinking structure maybe designed to have a desired amount of mechanical give (e.g., by usingepoxy, thermal pads, and the like having suitable mechanical propertiesto thermally connect different elements of the structure) so as toprovide the resonator with a greater amount of tolerance to changes inthe intrinsic dimensions of its elements (due to thermal expansion,magnetostriction, and the like) as well as external shocks andvibrations, and prevent the formation of cracks and other defects.

In embodiments where the resonator comprises orthogonal windings wrappedaround the magnetic material, the strips of conducting material may betailored to make thermal contact with the magnetic material within areasdelimited by two orthogonal sets of adjacent loops. In embodiments astrip may contain appropriate indentations to fit around the conductorof at least one orthogonal winding while making thermal contact with themagnetic material at at least one point. In embodiments the magneticmaterial may be in thermal contact with a number of thermally conductingblocks placed between adjacent loops. The thermally conducting blocksmay be in turn thermally connected to one another by means of a goodthermal conductor and/or heatsinked.

Throughout this description although the term thermally conductivestrips of material was used as an exemplary specimen of a shape of amaterial it should be understood by those skilled in the art that anyshapes and contours may be substituted without departing from the spiritof the inventions. Squared, ovals, strips, dots, elongated shapes, andthe like would all be within the spirit of the present invention.

Medical and Surgical Applications

Wireless power transfer may be used in hospital and operating roomenvironments. A large number of electric and electronic equipment isused in hospitals and operating rooms to monitor patients, administermedications, perform medical procedures, maintain administrative andmedical records, and the like. The electric and electronic equipment isoften moved, repositioned, moved with a patient, or attached to apatient. The frequent movement may result in problems related to powerdelivery to the devices. Equipment and electronic devices that are oftenmoved and repositioned may create a power cable hazards and managementproblem due to cables that become tangled, strained, unplugged, thatbecome a tripping hazard, and the like. Devices with a battery backupthat are capable of operating for a period of time without a directelectrical connection require frequent recharging or plugging andunplugging from electrical outlets every time a device is used orrepositioned. Wireless power transfer may be used to eliminate theproblems and hazards of traditional wired connection in hospital andoperating room environments.

Wireless power transfer may be used to power surgical robots, equipment,sensors, and the like. Many medical procedures and surgical operationsutilize robots or robotic equipment to perform or aid in medicalprocedures or operations. Wireless power transfer may be used totransfer power to the robotic equipment, to parts of the equipment, orto instruments or tools manipulated by the equipment which may reducethe potentially hazardous and troublesome wiring of the systems.

One example configuration of a surgical robot utilizing wireless powertransfer is shown in FIG. 18. The figure depicts a surgical robot 1806and an operating bed 1804. The surgical robot may be powered wirelesslyfrom a wireless source embedded in the bed, floor, or other structure.The wireless energy transfer may allow the robot to be repositionedwithout changing the position of power cables. In some embodiments thesurgical robot may receive power wirelessly for operation or chargingits battery or energy storage system. The received power may bedistributed to systems or parts such as motors, controllers, and thelike via conventional wired methods. The surgical robot may have adevice resonator in its base 1816, neck 1802, main structure 1808, andthe like for capturing oscillating magnetic energy generated by asource. In some embodiments the robot may be wirelessly powered from asource 1814 that is integrated, attached, or next to the operating bed.

In some embodiments the source resonator or the device resonator may bemounted on an articulating arm, or a moving or configurable extension asdepicted in FIG. 19. The arm or moving extension 1902 may be configuredto respond to positional changes of the robot, power demands, orefficiency of the wireless power transfer to reposition the source orthe device to ensure that adequate levels of power are delivered to therobot. In some embodiments the movable source or device may be movedmanually by an operator or may be automatic or computerized andconfigured to align or to maintain a specific separation range ororientation between the source and the device.

In embodiments the movable arm or extension may be used in situations orconfigurations where there may be a positional offset, mismatch, lateroffset, or height offset between the source and the device. Inembodiments the movable arm that houses or is used to position thesource or device resonator may be computer controlled and mayautonomously position itself to obtain the best power transferefficiency. The arm, for example, may move in all direction scanning themost efficient configuration or position and may use learning or otheralgorithms to fine tune its position and alignment. In embodiments thecontroller may use any number of measurements from the sensor to try toalign or seek the best or most efficient position including, but limitedto, impedance, power, efficiency, voltage, current, quality factor,coupling rate, coupling coefficient measurements, and the like.

In other embodiments the surgical robot may use wireless power transferto power motors, sensors, tools, circuits, devices, or systems of therobot, that are manipulated by the robot, or that are integrated intothe robot. For example, many surgical robots may have complex appendagesthat have multiple degrees of freedom of movement. It may be difficultto provide power along or through the various joints or moving parts ofthe appendages due to bulkiness, inflexibility, or unreliability ofwires.

Likewise, powering of the various tools or instruments necessary for aprocedure may pose reliability and safety problems with powerconnections and connectors in the presence of body fluids. A surgicalrobot may utilize one or more source resonator 1802 and one or moredevice resonators 1810, 1812 located in the appendages or tools to powermotors, electronics, or devices to allow movement of the appendages orpowering of tools, cameras, and the like that the robot manipulateswhich may be inside, or outside of a patient. The power may betransferred wirelessly without any wires regardless of the articulationor rotation of the appendages and may increase the degrees orarticulation capability of the appendages. In some embodiments thesources may be integrated into the robot and powered by the robot thatmay receive its own power wirelessly or from a wired connection. In someembodiments the source powering the appendages and the tools may bemounted on the operating bed, under the bed, or next to the patient.

As those skilled in the art will appreciate, the systems described andshown in the figures are specific exemplary embodiments and systems mayutilize any one of many different robot devices of various shapes andcapabilities, tools, and the like. Likewise the source may be mounted onany number of objects of various dimensions depending on the applicationand use of the robot. The source may be mounted on the operating roombed or pedestal as shown in the FIG. 18. In other embodiments a sourcemay be mounted in the floor, walls, ceilings, other devices, and thelike.

Wireless power transfer may be used to power or recharge movableequipment such as an IV or drug delivery racks or computer stands. Suchstands or racks are often repositioned temporarily or moved from onelocation to another with a patient. The electronic devices attached tothese racks often have battery backup allowing them to operate for aperiod of time without a direct electrical connection such that they canbe moved or repositioned and maintain their functionality. However,every time a traditional rack is moved or repositioned it needs to beunplugged and plugged back into an outlet for recharging or powering andthe cable must be wound or untangled from other cables.

The problems with traditional movable wired drug delivery, patientmonitoring, or computer racks may be overcome by integrating a wirelesspower transfer system to the devices. For example, sample embodiments ofa drug delivery rack and a computer rack are depicted in FIG. 20A andFIG. 20B. Device resonators 2008, 2006 and power and control circuitrymay be integrated or attached to the base or the body of the rack or thesupporting structure allowing wireless power transfer from a sourceresonator mounted into the floor, wall, charging station, or otherobjects. To be charged or powered the rack 2002 or stand 2014 may bepositioned in the proximity of the source, within a meter distance ofthe source, or within a foot separation of the source. The wirelesspower transfer enabled rack and the electrical equipment does notrequire plugging or unplugging or cable management. The wireless powertransfer enabled rack or electrical equipment may be powered bypositioning the rack or electrical equipment in a specific area of aroom or in proximity to the source that may be integrated into thefloor, carpet, walls, baseboard, other equipment and the like. In thisconfiguration, for example, a device or rack that may is only used forshort period of time to measure or diagnose a patient may be moved fromthe charging location and brought anywhere close to the patient to takea measurement and moved back into the charging location withoutrequiring precise positioning or plugging or unplugging of theequipment.

In some embodiments the device capturing wireless energy may requireadditional electric and electronic components in addition to aresonator. As described herein, additional AC to DC converters, AC to ACconverters, matching networks, active components may be necessary tocondition, control, and convert the voltages and currents from theresonator to voltages and currents that may be usable by the device tobe powered. In some devices and embodiments, the voltages and currentsof the resonator may be used directly without an additional conditioningor conversion step. Surgical tools such as cauterizers, electricscalpels, and the like use oscillating high voltages to effectively cut,stimulate, or cauterize tissue. The oscillating voltages on the deviceresonator may be directly used to power such devices reducing theirsize, cost, and complexity.

For example, in some embodiments a surgical tools such as a cauterizermay be fitted with a device resonator capable of capturing magneticenergy from one or more source resonators. Depending on the inductance,quality factor, resistance, relative distance to the source resonators,power output of the source resonators, frequency, and the like theparameters of the voltages and currents on the device resonator may beenough to directly cauterize or cut tissue. Voltages of 30 or more voltswith frequencies of 1 KHz to over 5 MHz may be generated on the deviceresonator and may be used directly as the output of the surgical tool.The oscillating electrical energy from the resonator may be directlyconnected to a cauterizing tip of the tool. In some embodiments theelectrical energy from the resonator may be coupled to the tool througha passive electrical network of components such as resistors,capacitors, and/or inductors. In other embodiments, the electricalenergy from the resonator may be coupled to the tool (e.g., cauterizingtip) directly without use of additional components prior to directconnection to the cauterizing tip, such as by a direct, wired electricalconnection from two terminals of the resonator to two terminals of thetool. In some embodiments monitoring circuitry, such as voltage sensoror other voltage or current sensing circuitry may integrated into thedevice resonator along with a wireless communication capability to relaythe measured values to a source. The source may monitor the receivedcurrent and voltage values and adjust its operating parameters tomaintain a specific voltage, frequency, or current at the device or toadjust the current or voltage is response to the operator input.

A block diagram of a wirelessly powered cauterizing tool is shown inFIG. 21. A device resonator 2106 configured to capture oscillatingmagnetic fields generated from the source resonator 2102 may beintegrated into the body 2104 of the tool. The oscillating electricalenergy from the device resonator 2106 may be directly connected to thecauterizing or cutting tip 2114 of the tool. An optional voltage andcurrent sensors 2110 may be integrated into the tool to monitor thevoltage and current at the output of the resonator and wirelesslytransmit the readings to the source 2102. The tool may therefore bepowered completely wirelessly from the source and may be able to receivepower over a distance of at least 5 cm away from the source resonator2102.

Wireless Power Transfer for Implantable Devices

In embodiments, wireless power transfer may be used to deliver power toelectronic, mechanical, and the like devices that may be implanted in aperson or animal. Implantable devices such as mechanical circulatorysupport (MCS) devices, ventricular assist devices (VAD), implantablecardioverter defibrillators (ICD), and the like may require an externalenergy source for operation for extended periods of time. In somepatients and situations the implanted device requires constant or nearconstant operation and has considerable power demands that requireconnection to an external power source requiring percutaneous cables orcables that go through the skin of the patient to an external powersource increasing the possibility of infection and decreasing patientcomfort.

Some implanted devices may require 1 watt of power or more or 10 wattsof power or more for periodic or continuous operation making aself-contained system that operates only from the battery energyimplanted in a patient impractical as the battery would require frequentreplacement or replacement after the implanted device is activated.

In embodiments, wireless power transfer described herein may be used todeliver power to the implanted device without requiring through the skinwiring. In embodiments wireless power transfer may be used toperiodically or continuously power or recharge an implanted rechargeablebattery, super capacitor, or other energy storage component.

For example, as depicted in FIG. 22A, an implanted device 2208 requiringelectrical energy may be wired 2206 to a high-Q device resonator 2204implanted in the patient 2202 or animal. The device resonator may beconfigured to wirelessly receive energy from one or more external high-Qresonators 2212 via oscillating magnetic fields. In embodimentsadditional battery or energy storage components may be implanted in thepatient and coupled to the device resonator and the implanted device.The internal battery may be recharged using the captured energy from thedevice resonator allowing the implanted device to operate for some time,even when wireless power is not transferred or is temporarilyinterrupted to the patient. The block components comprising anembodiment of a wireless power system are depicted in FIG. 22B. A deviceresonator 2204 implanted inside a patient and coupled to power andcontrol circuitry (not shown) that controls and tunes the operation ofthe resonator may be coupled to a rechargeable battery or other energystorage element 2210 that is also implanted in the patient. The energycaptured by the device resonator may be used to charge the battery orpower the implanted device 2208 directly using the captured energy thatis generated by an external resonator 2212.

The wireless energy transfer system based on the high-Q resonatorsources and devices described herein may tolerate larger separationdistance and larger lateral offsets than traditional induction basedsystems. A device resonator implanted in a patient may be energizedthrough multiple sides and angles of the patient. For example, a deviceresonator implanted in the abdomen of a patient may be energized with asource from the back of the patient. The same device resonator may alsobe energized from a source positioned in the front abdomen side of thepatient providing for a more flexible positioning and orientationconfiguration options for the source.

In embodiments the resonator and the battery may be integrated with theimplanted device into one substantially continuous unit. In otherembodiments the device resonator and the battery may be separate fromthe implanted device and may be electrically wired to the device. Theresonator may be implanted in a different part of the body than thedevice, a part of the body that may be more accessible for an externalsource resonator, less obtrusive to the patient, and the like. Inembodiments the device resonator may be implanted in or close to thebuttock of the patient, or the lower back of the patient, and the like.In embodiments the size of the resonator and placement may depend on theamount of power required by the implanted device, distance of wirelesspower transfer, frequency of power delivery or recharging, and the like.In some embodiments, for example, it may be preferable to use a deviceresonator that is smaller than 7 cm by 7 cm such that it may be easierto implant in a person while capable of delivering 5 watts or more orpower at a separation of at least 2 cm.

In embodiments the implanted device resonators may comprise a round orrectangular planar capacitively loaded conductor loop comprising fiveloops of a Litz conductor coupled to a capacitor network as describedherein. In embodiments it may be preferable to enclose the implanteddevice resonator in an enclosure comprising mostly nonmetallic materialsto minimize losses, or an enclosure which has at last one side thatcomprises non-metallic material.

In embodiments, an implanted medical device may comprise an inductiveelement comprised of any number of turns of Litz wire, magnetic wire,standard wire, conducting ribbon such as a trace on a printed circuitboard, and the like. In embodiments, implanted medical devices maycomprise magnetic materials, ferrites, and the like and may be optimizedfor specific frequencies or frequency ranges such as 13.56 MHz or 100 ormore kHz.

In embodiments, a patient may have more than one implanted device thatis wirelessly powered or recharged. In embodiments, multiple devices maybe powered or charged by a single source or by multiple sources. Inembodiments, multiple devices may operate at the same resonant frequencyor at different resonant frequencies. Either the source, repeater ordevice resonators may tune their frequency to receive or share power.

In embodiments, the magnetic resonators may comprise means forcommunication with other magnetic resonators. Such communication may beused to coordinate operation of wirelessly powered medical devices withother wireless systems. In an exemplary environment, an implanted deviceresonator may adjust its operating parameters in the vicinity of ahigh-power source of another wireless power system. In an embodiment, amedical device source may communicate with another wireless power sourcein a region and communicate with a patient to avoid or exercise cautionin such a region.

Embodiments comprising high-Q device resonators and optionally high-Qsource resonators allow for more efficient wireless power transfer andcan tolerate larger separation distances and lateral offsets of thesource and device resonators than traditional induction based systems.The high efficiency of the wireless power transfer systems describedherein reduces heating and heat buildup in resonators which may be ofcritical importance for resonators implanted in a patient. The describedresonators may transfer 5 watts or more or power while withoutsignificant heating of the elements such that the temperature of thecomponents does not exceed 50 C.

Tolerance to separation distance and lateral offset between an externalsource resonator and an implanted device resonator allows greaterfreedom of placement of the source resonator. The use of wireless powertransfer systems as described herein may also provide greater safety tothe patient since movements or displacements of the source resonatorwill not disrupt the power transfer to the implanted device.

In embodiments power may be transferred to the implanted deviceresonator from a source resonator that is worn by the patient in abackpack, hip pack, article of clothing and the like. For example, asdepicted in FIG. 23A, source resonators 2304 may be embedded in clothingand worn by a person 2302, the source resonators 2304 may be wired topower and control circuitry and a battery (not shown) to deliver thepower to the implanted device resonator (not shown). In otherembodiments the source resonators and power source may be contained in abackpack, or a bag as depicted in FIGS. 23B, 23C, and 23D. A backpack2306 or other bag 2312 may be integrated with a source resonator 2308,2314 in a location such that when worn by the patient the sourceresonator will be in substantial alignment with the implanted deviceresonator in the patient. For example, for a device resonator implantedin the buttock or lower back, a backpack with a source resonatorintegrated into the lower back portion provides for substantialalignment of the source and device resonators when the backpack is wornby the patient as shown in FIG. 23D. In embodiments the backpack or bagmay further comprise additional device resonators 2310 for wirelesscharging of the internal energy storage or battery that is inside thebag. The backpack may be placed near an external source resonator orcharging station and charged wirelessly. In some embodiments the sourceand device resonators of the backpack or bag may be the same physicalresonator that alternates function between a source and a devicedepending on the use.

In embodiments external source resonator may be integrated intofurniture such as chairs, beds, couches, car seats, and the like. Due tothe tolerance to misalignment of the high-Q wireless power transfersystem described herein, device resonators may be integrated into thefurniture in areas of relative proximity to the implanted deviceresonators (i.e. within 25 cm) and transfer power to the implanteddevice resonator and implanted device while a patient is working at adesk and sitting in a chair, sitting in couch, driving, sleeping, andthe like.

In embodiments the wireless power transfer system for implantabledevices may include repeater resonators. Repeater resonators may be usedto improve the energy transfer between the source and device resonatorsand may be used to increase the overall coupling and power transferefficiency. As described herein a repeater resonator positioned inproximity to a device resonator may increase the wireless power transferefficiency to the device resonator from a distal source resonator.

In embodiments the repeater resonators are positioned to improve theenergy transfer between the source and the device. The position of therepeater resonators that provides the highest improvement in efficiencyor coupling may depend on the application, size of the resonators,distance, orientation of resonators, location of lossy objects and thelike. In some embodiments an improvement in wireless energy transferefficiency may be obtained by positioning the repeater resonators inbetween the source and device resonators. In other embodiments it may bebeneficial to position the repeater resonators angled or further awayfrom the source than the device. The exact placement of repeaterresonators may be determined experimentally with trial or error, withsimulation, or calculations for specific configurations, power demands,implanted devices and the like. In embodiments the repeater resonatorshould be sized and positioned to improve the coupling between thesource and the device by at least 10%.

In embodiments of a system, repeater resonators may be positioned orlocated internal to the patient, or they may be located external to thepatient, or a system may have both internal and external resonators. Arepeater resonator may be internal or implanted into a patient. Arepeater resonator may be implanted under the skin of a patient toimprove the coupling to a device resonator. Since a repeater resonatordoes not need to be connected to a device it may be easier to positionor implant a larger repeater resonator than a device resonator that isconnected to an implanted medical device. The device resonator may haveto be implanted deeper inside a patient due to distance limitations orsize limitations between the resonator and the medical device. Therepeater resonators may comprise loops of a conductor like Litz wireconnected to a network of capacitors. The repeater resonator may beencased in flexible material or packaging such as silicon, or otherimplantable plastics. The whole structure may be implanted inside thebody under the skin to provide fine tuning of the wireless energytransfer between the external source and the implanted device.

In embodiments repeater resonators may be positioned outside, externalto a patient into articles of clothing, packs, furniture and the like.For example, larger repeater resonators with a diameter of 20 cm or moremay be integrated into an article of clothing such as a vest, robe, andthe like or an attachable pad and worn by the patient such that therepeater resonator overlaps or is in close proximity of the implanteddevice resonator. The repeater resonator may be completely passive or itmay have additional circuitry for power and control. Locating therepeater resonator in close proximity of the implanted device resonatoreffectively increases the size of the implanted resonator to a size thatis substantially or close to the size of the repeater resonator and mayallow more efficient wireless power transfer to the implanted deviceresonator and device over a larger distance. The repeater resonator maybe much larger than the resonator that is practical for implant in aperson.

In embodiments multiple repeater resonators, internal or external to thepatient, may be arranged in an array or a pattern around the body toallow wireless energy transfer from a source to an implanted device overa large range of offsets. Each repeater resonator may be specificallytuned or configured to provide adequate coupling to an implanted deviceresonator based on its relative location from the device resonator.

In embodiments a room, a bathroom, a vehicle, and the like may be fittedwith large source resonators to transfer sufficient power to the patientvia the repeater resonator allowing continuous power transfer andrestrictions on mobility while showering, sleeping, cooking, working,and the like.

In embodiments the repeater resonator may include wireless powerconverter functionality for translating wireless energy withincompatible parameters to oscillating magnetic fields with parameterscompatible with the implanted device resonator. A wireless powerconverter resonator integrated into a vest, bag, and the like may beworn by the patient and capture wireless power from a variety of sourcesand transfer the captured wireless power to the implanted deviceresonator with parameters compatible with the implanted deviceresonator. In embodiments the wireless power converter may be configuredto capture wireless power from solar energy, an RF source, movement,motion, and the like. In embodiments the repeater resonator may act as apower converter that limits the power delivered to the implanted deviceresonator preventing too much power from being delivered to the patient.

In embodiments, a repeater resonator or wireless power converter mayhave auditory visual or vibrational alerts when it no longer receivespower. A repeater resonator may detect when it is not coupled to theimplanted device or may detect that it is not receiving enough powerfrom an external source and may be configured to alert the patient.

In embodiments a fully integrated external source resonator, may beencased in a waterproof enclosure, including a rechargeable battery, RFamplifier, and a source resonator. The integrated source and circuitrymay be of a form factor that may be attached with a belt or a strapallowing the patient to go swimming or take a shower with the integratedsource intact. The integrated source and circuitry may also have aninternal battery charging circuit & rectifier, so it can be wirelesslycharged by switching the resonator and electronics to capture mode.

In embodiments of the system, the device and source and repeaterresonators may include a tuning capability to control heat dissipationin implanted resonators. During wireless energy transfer electriccurrents and voltages induced in the device resonator by the magneticfields of the source resonator may cause heating of the resonatorelements due to ohmic losses, internal losses, and the like. Animplanted resonator may have restrictions on the amount of heat it cansafely dissipate before raising the temperature of the surroundingtissue to an undesirable level. The amount of power that may be safelydissipated may depends on the size of the resonator, location of theresonator and the like. In some systems one or more watts of power maybe safely dissipated in a patient.

A source or repeater resonator, which is external to a patient, may bedesigned to tolerate higher levels of heat dissipation. The externalsource or repeater resonator may have higher limits of safe powerdissipation or heating. A source or repeater resonator that is externalto a patient may be designed to safely dissipate 5 watts of more of heatand may include active cooling means such as fans, or water cooling andmay be able to safely dissipate 15 watts or more of power. Inembodiments a wireless energy transfer system may control the amount ofheat dissipated in the device resonator. Since a source or repeaterresonator may be able to tolerate more heat dissipation than a deviceresonator, a wireless energy transfer system may be tuned to reduce theheat dissipation at the device resonator. A system tuned to reduce heatdissipation at the device may have higher overall heat dissipation withthe increased heat dissipation occurring in the source or repeaterresonator.

The heat dissipation in a device resonator may be controlled by reducingthe electric currents oscillating in the implanted device resonator. Thecurrents in the device resonator may be controlled by tuning theresonant frequency of the resonator. The currents in the deviceresonator may be controlled by tuning the impedance of the resonator.

In embodiments the device resonator may comprise one or more temperaturesensors along with monitoring circuitry and control logic. Upon thedetection of a temperature threshold the monitoring and controlcircuitry may detune the resonant frequency away from the resonantfrequency of the source or repeater resonator. The monitoring andcontrol circuitry may detune the resonant frequency above the resonantfrequency of the source or repeater resonator. The monitoring andcontrol circuitry may detune the resonant frequency below the resonantfrequency of the source or repeater resonator. The device may be detunedincrementally until the temperature of the device resonator stabilizes.In embodiments the frequency may be detuned by 1% or more or inincrements of 1 kHz or more.

As those skilled in the art will appreciate, the resonant frequency maybe changed with a variable component in the device resonator such as avariable capacitor, inductor, a bank of capacitors, and the like.

In embodiments the detuning of the resonant frequency of the deviceresonator may decrease the efficiency of energy transfer between thesource or repeater and device. To maintain the same level of powerdelivered to the device the source may be required to increase the poweroutput to compensate for the reduction in efficiency. In embodiments thedevice resonator may signal the source resonator of a temperaturecondition that may require an adjustment of its resonant frequency andalso the power output of the source resonator.

Similarly to controlling the resonant frequency, the effective impedanceof the device resonator which may affect the currents and voltages inthe resonator may be controlled by adjusting components of the resonatorsuch as inductance and the capacitance. In embodiments the impedance maybe tuned by changing the power requirements of the device, or bycontrolling the switching frequency, phase, and the like of therectifier or the switching dc to dc converter of the device.

A device resonator may continuously monitor the temperature of thecomponents and monitor and trends of the temperatures and adjust thefrequency and values of components to stabilize the temperature.

In embodiments the wireless energy transfer system may be tuned toreduce the heat dissipation in device resonators and distribute the heatdissipation to repeater resonators. Implanted repeater resonators may belarger than the device resonators and may be able to dissipate more heatthan a smaller device resonator. Likewise a repeater resonator may beimplanted closer to the skin of a patient thus allowing the repeaterresonator to be cooled through the skin with external cooling packs orpads worn by the patient.

While the invention has been described in connection with certainpreferred embodiments, other embodiments will be understood by one ofordinary skill in the art and are intended to fall within the scope ofthis disclosure, which is to be interpreted in the broadest senseallowable by law.

All documents referenced herein are hereby incorporated by reference intheir entirety as if fully set forth herein.

What is claimed is:
 1. A wireless energy transfer apparatus for animplantable medical device, the apparatus comprising: a device resonatorconfigured to supply power for a load of the implantable medical deviceby receiving wirelessly transferred power from a source resonatorcoupled with a power source; a temperature sensor positioned to measurea component of the apparatus; a tunable component coupled to the deviceresonator to adjust a resonant frequency of the device resonator, aneffective impedance the device resonator, or both; and control circuitrycoupled with the temperature sensor and the tunable component; whereinthe control circuitry is configured to, in response to detecting atemperature condition using the temperature sensor positioned to measurethe temperature of the component of the apparatus, (i) tune the tunablecomponent to adjust the resonant frequency of the device resonator, theeffective impedance of the device resonator, or both, and (ii) signalthe source resonator regarding the temperature condition to cause anadjustment of a resonant frequency of the source resonator, a poweroutput of the source resonator, or both.
 2. The wireless energy transferapparatus of claim 1, wherein the control circuitry comprises acommunication controller coupled to wireless communication circuitryuseable to signal the source resonator regarding the temperaturecondition.
 3. The wireless energy transfer apparatus of claim 1, whereinthe tunable component comprises a variable capacitor.
 4. The wirelessenergy transfer apparatus of claim 1, wherein the tunable componentcomprises a bank of capacitors.
 5. The wireless energy transferapparatus of claim 1, wherein the tunable component comprises aninductor.
 6. The wireless energy transfer apparatus of claim 1, whereinthe device resonator has a Q>100.
 7. The wireless energy transferapparatus of claim 1, wherein the control circuitry is configured tocontinuously monitor temperatures of the component of the apparatus andtrends of the temperatures of the component of the apparatus, and adjustthe tunable component to stabilize the temperature of the component ofthe apparatus.
 8. The wireless energy transfer apparatus of claim 7,wherein the tunable component comprises at least one inductor or atleast one capacitor of the component of the apparatus that thetemperature sensor is positioned to measure.
 9. The wireless energytransfer apparatus of claim 1, wherein the device resonator is tunedincrementally until the temperature stabilizes.
 10. The wireless energytransfer apparatus of claim 9, wherein the device resonator is tuned inincrements of 1 kHz or more.
 11. The wireless energy transfer apparatusof claim 1, wherein the tunable component is adjusted to tune theresonant frequency of the device resonator to be above the resonantfrequency of the source resonator.
 12. The wireless energy transferapparatus of claim 1, wherein the tunable component is adjusted to tunethe resonant frequency of the device resonator to be below the resonantfrequency of the source resonator.
 13. The wireless energy transferapparatus of claim 1, wherein the tunable component is adjusted tomaintain the temperature of the component of the apparatus below 50degrees Celsius.
 14. The wireless energy transfer apparatus of claim 1,comprising a rechargeable battery, wherein the device resonator iscoupled with the implantable medical device and supplies power to theload through the rechargeable battery.
 15. A wireless energy transfersystem comprising: the wireless energy transfer apparatus of claim 1;and the source resonator; wherein the device resonator and the sourceresonator are tuned to increase overall heat dissipation by reducingheat dissipation occurring in the device resonator and increasing heatdissipation occurring in the source resonator.
 16. The wireless energytransfer system of claim 15, comprising an active cooling system for thesource resonator.
 17. The wireless energy transfer system of claim 16,wherein the active cooling system for the source resonator comprises afan.
 18. The wireless energy transfer system of claim 16, wherein theactive cooling system for the source resonator is configured to safelydissipate 5 watts or more of heat.
 19. The wireless energy transfersystem of claim 16, wherein the active cooling system for the sourceresonator comprises a water cooling system.
 20. The wireless energytransfer system of claim 16, wherein the active cooling system for thesource resonator is configured to safely dissipate 15 watts or more ofpower.